Blinkies look like these:
While stamps look like these:
They're just fun ways to add funny stuff to a user's profile :o though, some stamps/blinkies could be used to add some extra info in a fun way (like a user's fandoms, interests, pronouns, etc.).
If you wanna add them to your profile (or to forum replies like this one), websites specifically made for blinkies/stamps (like this one) will have the code already set up for you. All you have to do is copy-and-paste (note: choose the link that has <a>, <img>, or other similar HTML tags). Although, in the case of forum replies, you gotta make sure you hit the <> button before adding any HTML code :0
I will say, however, that apparently certain sites that host blinkies and stamps are known to eventually stop working on SpaceHey :/ dunno why. If your blinkies/stamps ever suddenly disappear, I'd suggest downloading the images yourself and putting them onto an image hosting site. From there, you can use the <img> tag (AKA <img src="*insert direct image/gif URL*">) and won't have to worry about them disappearing again