Learn Arabic (Modern Standard): سنرجع من الرحلة غدا.

The future tense is made by attaching the prefix سـ (sa-) directly to the front of the present tense verb. Here, it is attached to نرجع (we return) to make سنرجع (we will return).

Could we use "سوف" instead of the prefix "سـ" here?

Yes! You can say سوف نرجع (sawfa narji'u). Both express the future tense and mean the exact same thing. The only difference is that سـ attaches to the beginning of the verb, while سوف is written as a separate word right before the verb.

As a quick refresher, how can we tell that "نرجع" means we return?

In the present tense, verbs starting with the letter نـ (noon) correspond to "we". If you wanted to say "I will return", you would change the first letter to an alif: سأرجع (sa'arji'u).

Why does the word for tomorrow (غدا) end with two little lines over an alif?

Those two lines are a double-fatha marker (tanween) that adds an "-an" sound to the end of the word, making it pronounced ghadan. In Arabic, time words often take this "-an" ending when they are used to show when an action happens.