Good evening Lynne, welcome to this great website & forum.
You can search the huge database quite easily from the Parish Records "button" on the blue menu bar across the top of the screen. When searching at first keep it vague without inputting too much info; better to see everything thats a "maybe" rather than inadvertantly filter out the "probables". I've searched for all records for "John Symonds" but have entered your "1805" date plus/minus 5 years. I've also ticked the "SOundex" box to help give spelling variations, although this isn't always as effective as it could be. This still gives 18 PRs to consider !

Never assume the dates given from Censuses are very accurate, they only recorded what the people believed or wanted to believe, lady's ages are particularly "vague"..

Anyhow from those 18 this looks a possible, although no second name so not sure about the B.

Record_ID: 433453
Entry_Number:
Year: 1807
Month: May
Day: 24
Parents_Surname: SIMMONDS
Child_Forenames: John
Fathers_Forenames: Edward
Mothers_Forenames: Rose
Mothers_Surname:
Residence:
Occupation:
Officiating_Minister: Tho[ma]s Davies Minister
Event: Baptism
Memoranda:
Notes:
Register_Reference: P241 IN 1/3
Page_Number:
Parish_Chapel: Oxenhall
Soundex: S553

How's that seem ?

Now to find a Marriage.
Assume he's 20 years older, search again but using the date "1837" plus/minus 5 years, and the Marriage Filter. However for some reason this hasnt found a likely Marriage. A few months ago I'd have just searched again but assumed age "1847". Then I "discovered" the rather clever Advanced Search feature.
If you look towards the bottom of the Parish Records search page you'll see "Advanced search". Click this to change page. Select "Marriage" from the dropdown menu and hit return to load the Marriages page. Now click "search".
By entering "John" and "Martha" in you'll get all those Marriage combinations in the database, possibly too large but I ALWAYS think better & safer to start wide then narrow the search.

This gives a list of 261 Marriage Records !. Select "100" results from dropdown menu to give a large table. Click on the heading "Year", this will sort them chronologically. Scan thro the tables to wards the 1830s results looking for Symonds. When you see a likely result click onto the lefthandmost "page" icon to give the full details. Alternatively click on any heading, for example Groom's Surname and it will be sorted in alphabetical order that way.

This way, and thankfully for us, you'll find the single only possible "Symonds" in the whole set of results:

Record ID 1014251
Entry Number
Year 1833
Month Apr
Day 3
Grooms Surname SIMMONS
Grooms Forenames John
Grooms Age
Groom Condition bachelor
Grooms Occupation
Grooms Residence Glos St Nicholas
Grooms Fathers Surname
Grooms Fathers Forenames
Grooms Fathers Occupation
Brides Surname TAYLOR
Brides Forenames Martha
Brides Age
Brides Condition spinster
Brides Occupation
Brides Residence Glos St Nicholas
Brides Fathers Surname
Brides Fathers Forenames
Brides Fathers Occupation
Licence or Banns Banns
Date of Banns
Signature or Mark He marks she signs
Witness 1 George Fisher
Witness 2 Elizabeth Fisher
Other Witnesses J Wheeler clerk
Officiating Minister J Davies incumbent
Event Marriage
Memoranda
Notes
Register Reference P154/15 IN 1/13
Page Number 22
Parish Chapel Gloucester St Nicholas

So again the Soundex system, albeit usefull, has proven to not work too well. Hence my preference wherever practical for not using it, I tend to only apply methodical date limits then look at all the possibles within that dateband, before moving onto the next say 20 years dateband. Names were often spelt vary "oddly" to put it mildy !

The Advanced Search feature is really useful and very effective with practice.

This may be Martha's Baptism, certainly the most likely from the Forest PRs rather than Gloucester-way. Shame no clues as to parent's on the Marriage Record:

Record_ID: 250704
Entry_Number:
Year: 1796
Month: Mar
Day: 28
Parents_Surname: TAYLOR
Child_Forenames: Martha
Fathers_Forenames: John
Mothers_Forenames: Lydia
Mothers_Surname:
Residence: Redmarley D'Abitot
Occupation:
Officiating_Minister: John Howe Rector
Event: Baptism
Memoranda:
Notes:
Register_Reference: P265 IN 1/2
Page_Number:
Parish_Chapel: Redmarley
Soundex: T460

Re their Marriage, wonder who the witnesses are ?

Searching gives 43 "George Fisher" PRs for the whole database, most are from t'other side of the Forest, this standsout re locality, not to mention his bride:

Record_ID: 94524
Entry_Number: 19
Year: 1816
Month: Mar
Day: 20
Grooms_Surname: FISHER
Grooms_Forenames: George
Grooms_Age:
Groom_Condition:
Grooms_Occupation:
Grooms_Residence: Of this Parish
Grooms_Fathers_Surname:
Grooms_Fathers_Forenames:
Grooms_Fathers_Occupation:
Brides_Surname: TAYLOR
Brides_Forenames: Elizabeth
Brides_Age:
Brides_Condition: Spinster
Brides_Occupation:
Brides_Residence: Of this Parish
Brides_Fathers_Surname:
Brides_Fathers_Forenames:
Brides_Fathers_Occupation:
Licence_or_Banns: Banns
Date_of_Banns:
Signature_or_Mark: Both sign
Witness_1: William Taylor
Witness_2: Martha Taylor
Other_Witnesses:
Officiating_Minister: James Commeline Rector
Event: Marriage
Memoranda: With consent of Parents
Notes:
Register_Reference: P265 IN1/10
Page_Number: 7
Parish_Chapel: Redmarley
Soundex_Groom: F260
Soundex_Bride: T460

Note the witnesses here !

No doubt you'll find more relevant PRs yourself. Happy hunting !

Finally, please also search this forum itself, often others have already researched "your" subject. Also please look at the rest of the site, theres a huge amount of other resources freely available, such as old documents (Wills, Inquests), E-Books, newpaper clippings, photos, maps etc etc.
Hopefully this sounds reasonable to you ?.
Of course the more time you spend searching the PRs the easier it becomes.