Hi 'unfamiliar' and welcome.
You will have to decide the amount of time that you want to invest in getting your 'fair market value'.
With a minimum amount of time you could go to a bricks and mortar stamp store, now becoming more rare, and have them look at them and give you an offer. The amount will typically be a lot less money than other options.
Then in order of your investment in time you will typically gain more money by:
1. Contact a stamp auction house that specializes in the countries you have (Google search), tell them roughly what you have, and if they decide to include them in their next auction then you will have to pay to have them registered and sent to them. They will take a commission on a sale, and send you the remainder.
2. Breaking the collection into country lots, scanning them and placing them on
ebay or another auction site with a minimum bid of $1.00 and hoping that collectors will see the valuable stamps and complete on price.
3. Go to your local library and using the Scott stamp catalogues, determine what you have, and what their catalogue value is. Keep in mind that the market price for stamps is typically 15-30% of their catalogue value.
Finally you could go to your local stamp club, that would typically meet once a month or more often and show your stamps to them to get some knowledge as what you have so that you can decide what route to take with them.
Good luck!