You can either upload a copy of the db, or the part which you are having a problem with - with sensitive data removed of course.
Or you can use the database documenter to provide the documentation - if you click on options your can remove elements you don't want to make the report smaller - so just to provide a list of fields and their types turn everything off except this option. This generates a report which you can then export to word etc which you can then edit to remove pagebreaks etc.
Normally on this forum you would present tables within the post along the following lines:
myTable
ID autonumber PK
FName text
OtherID long FK
With regards relationships, I would include a screenshot of your relationships screen - ideally laid out neatly with all fields showing.
Db structure is typically defined by what it is required to do and under what conditions (single user/multiuser etc), so include a paragraph about this as well.
If the post is getting too long, I would put into a separate document as an attachment
