Welcome,
You received some good advice from some good members. I got into collecting as a child in the early '60s via a similar gift. I thought that I could expand on a few possible avenues for you.
Main choices:
A. Leave the collection for your grandchildren.
B. Give or donate it to someone who shows an interest.
C. Sell it for a token amount on Craigslist, Facebook, etc.
D. Start a collection.
If D., I would consider the following:
Put the stamped envelopes(keep the torn ones for now) together and call it your new "Cover" collection. Go to
ebay to see others.
Assemble the stamps into general collections after tossing the damaged ones: Definitives, Commemoratives, Airmails, Back-of-Book(Postage Due, Special Delivery, Revenues, etc.) and foreign.
Start your stamp collection(s) by getting the following:
Free catalog from Mystic Stamp Co.
Perforation gauge
(esp. for your 1 and 2 cent Franklins and Washingtons)
Either a stamp album and/or more black Vario pages.
For online resources you can't do better than this Forum and Stamp Smarter. Later on you can seek out a stamp club in your area.
Hope this helps get you started. Good luck.
Greg K.