As in English, there is no particular verb form to express future, which you could find in, for instance, romance languages. Instead, we use auxiliary verbs to express this.
Anders ska(ll) gå på musikal.
Anders is going to a musical.
Ska expresses a strong intention or demand. The future action is more or less decided.
Ska is traditionally written skall which is slowly disappearing. It’s rather individual how you want to write it. For formal language, the latter is advised.
Imorgon kommer det att regna.
It will rain tomorrow.
The intentions expressed with komma att are not as written in stone like skola. It expresses a kind of prediction.
Jag tänker gå en kurs i Svenska.
I’m going to / planning to take a course in Swedish.
This way of talking about the future expresses a kind of plan to do something.
Remember that the explanations are tips for you how to use them. The borders are, of course, a bit fuzzy. You’ll develop a feeling for these expressions over time.
You can also use present tense to talk about something you will be doing in the future.
Snart går jag.
I will be going / leaving soon.