Can this be the future tense or does it have to be present tense (i.e. today is your birthday)?
Just as in English you can use the present tense when referring to the future, especially when it is certain.
I've noticed this too with Swedish; there are different ways you can actually translate a present tense verb into English.
Take for example: "Jeg går til butikken. (NO)/Jag går til butikken. (SV)"
It can be "I am going to the shop." I'm currently existing in the process of going.
It can also be "I go to the shop." That's more generic, I'd probably use that for casual conversation.
And then there's the special one, where, depending on the verb's context, it can hint at a future tense... In the sentence given above, this is also translated as "I am going to the shop" formally. Often, especially in spoken conversation, you'll find the future tense hinted by a conjunction in English: "I'm going to the shop."
Hope this clarifies!!
Can you use om here instead of på? Im still a little confused on when to use what word
"På" is your only option here. Prepositions are tricky, particularly when it comes to time.
No, not in this context.
However, if you were asking someone what they wanted for their birthday, you'd say "Hva ønsker du deg til bursdagen din?".