Unlock Steam Account

you must buy something and after 1 month you can start trading

nope, and s/he can't use market right now

s/he should make a store purchase. if it's just for trading purposes, activating a gift also works

He'll need to purchase something from the store.

send him gun monkeys and wait month :D

Market won't be available to the account if it was created today.
Store purchase or redeeming a gift should do it.

ppl should really learn to read, next to the info of the restriction is a link which leads to an info page about what the ristriction means...

https://support.steampowered.com/kb_article.php?ref=1047-EDFM-2932#nottrusted
(FYI: the whole page is important)

You can speed up the process!!!!....................................just find Gabe and buy him a Burger.

Oh, I remember when it all begun!
It was after Alien Swarm was announced being the first Free-to-play game on steam!The servers became overloaded with new users, so Valve decided that only those who ever bought anything on steam (market and wallet didn't exist yet!it meant a game) could add friends, be part of a group, etc.
Alien Swarm was a dead game few months after, a very good game but very repetitive, also very exploitable requiring literally no skills to do so, but the restriction stayed.
Then, years late, DotA 2 was announced as closed beta, also TF2 became free-to-play, meaning that users who never spent any money on games could spend money on microtranstions.A lot of these new players raged because they could not add friends and talk to people on steam, only in-game, but soon they would learn to love Gaben and his team!
Now you only need to buy anything once with real money to have access to market!And don't even need to buy anything to have access to the rest of the community!