Several different areas that philatelics collect - the stamps themselves, the cancellation, the covers.
Some are interested in the post office, some on the date ( stamps and cancellations can be scarcer on certain key dates or when there was a strike )
Then you have the varying plates of the Penny Red - you need to take a magnifying glass and look in the left and right margins.
Good stamps are obviously the Penny Blacks and other Victorian ones but then Edward VII, George's V and VI also have stamps which are highly sort after, usually from 1/- and upwards and generally in unused condition, although some people collect the war period issues and cancels.
If you take a photo of some i can give you a rough guide. Then tell me the county and i'll let you know the best auction house to visit.