I usually interpret likes received as either acknowledgement, agreement, or that the person who liked my post thinks that what I said is interesting. And it does give me a good feeling to see that people like what I have to say. Since it is similar to someone giving you a compliment.
For suggestions, likes mainly mean that people support your suggestion. And it is good to see your suggestion get a lot of likes for this reason because likes=support here.
My posts generally tend to be large with a few paragraphs even with simple topics for some reason, so it does mean a fair deal when people like large posts that I make, since it means I didn't waste my time making that post to explain many details about my thoughts or feelings on certain things.
For when I give likes, it usually means that I agree with what you're saying, that what you're saying is interesting, or if the context is humorous that it made me laugh. Similar to what it is like to receive likes. When someone writes a compliment for me or says something very nice directly to me that makes me feel good, I will usually give a like as a way to say "Thank You" or "You're Welcome" depending on the context.
Sometimes if someone posts something that's very close to my own thought on a subject in a discussion area, I will like that person's post to show that I agree with that statement because to add my own would be redundant when 95% or more of that person's post was similar to what I would've said.
Same case for suggestions. When I like a suggestion I support it. Regardless of whether I reply or not.
When I 1st joined the forums I confess during my 1st 1 or 2 months, I didn't give out likes, but this was more due to how I was still getting used to the forums and was still very shy when it came to posting on Non-Terraria threads, or other people's profiles (I'm shy IRL which carries over to anytime I join something. I think for the most part I've broken out of my shell on TCF, but I'm careful about what I post and I don't try to seek out too much attention). After I got out of my extremely shy phase, I started giving out likes more often. I believe I give out a moderate amount of likes overall and hope that the likes I give make the recipients feel good.