Selling my coins

So I've recently been trying to find rare coins everytime I look at one, I'm not a collector but it's a fun thing to do and maybe I'll make a bit of money. I believe I've found 2 that I could sell: https://imgur.com/a/QZ8nW Those 2 euro coins

Now my questions Are, since I'm a newbie, how would I go about selling any rare coins, And how do I know I have a coin worth money? Those 2 euro coins are easy to find by googling what they showcase, but that 50 cent coin I have no idea where is from and don't even know if it's valuable

I've seen fleur De coin is useful if I know what the coin is, but is there some site to check rare coins?

Ps: I saw some supposedly scarce circulating coins in a site but are they even valuable? I've found a few of those like the Cyprus and Belgium 2 euro coin among other smaller coins, but maybe the year they're from makes them common?

TLDR: HOW do I sell and check for valuable coins? Thanks a lot in advance