Help me understand leveling up

http://www.sgtools.info/sent/wwigleg2/newestfirst

FAQ. Look for "bundle games".

levels and cv
your real sent cv
"bundled" games give you 15% of the US store price - bundle list

You only get a portion of the value of games that have been highly discounted or part of bundles. The exact percentages are in the FAQ. https://www.steamgifts.com/about/faq

Also small sidenote but CV is added to your account after they're marked as received from the winner so anything at the "Awaiting Feedback" stage does not yet count.
Welcome to Steamgifts! 👍

well, what the rest said... and then, there is this
a complete (i hope) list of every important and interesting discussion on SG

You give, you mark as receceived, you give again
https://www.youtube.com/watch?v=tl4SsaOJlAc

And finally: don't look too much into levelling. It can be a fun game, but there is no actual pay-off. It is barely more than the Steam profile levelling game.
Unless you grind all the way up to level 10, spending an assload of money, so you can see the small button that gives you free ice cream.