I'm just a student like you, but I'm pretty sure "willkommen" is rarely if ever used as a response to thank you. For one thing, I never heard it said as a response to my "dankes" when I was in Germany (just a couple of times.) It also seems to be confirmed by at least one native speaker I found in a search on line. Here is his response:
You can use "Bitte", "Bitteschön", "Gern geschehen" or "Nichts zu danken".
"Bitte" and "Bitteschön" are almost equal, but bitteschön is a bit more polite. You can pretty much always use them but they are mostly used for very small favors. Bitte and bitteschön can also be used like "here you go", like when you hand something to someone.
"Gern geschehen" and "Nichts zu danken" would be used if someone thanks you for a larger favor like when you gave them a present or explained how to get somewhere or things like that. But in that context you could also use bitte or bitteschön
The only thing that might sound weird would be if you are holding a door open for someone or sitting at the breakfast table and pass the butter to someone and then say "Nihcts zu danken". It's not wrong, it's just a bit too much.
me (I'm German)