In German there are 6 tenses as far as I know, but I always wonder how to describe very near future e.g.
I’ll be showing you (something) in this video.
What are the best words to tell the above sentence in German?
I’m afraid it’s not just a question about near or distant future. You go with present tense when you speak about a future event in a, say, neutral but assured way.
Ich bin sofort da.
Ich mache das gleich.
Heute abend geh ich früh schlafen.
Morgen räum ich die Garage auf.
Nächste Woche laufe ich einen Marathon.
In zwei Monaten fahre ich in Urlaub.
Nächstes Jahr ziehe ich nach Berlin.
The more distance is between now and the designated future time, the less likely it is that you can say for sure that it is going to happen. Also some things are not really determinable, even if it’s supposed to happen today or tomorrow.
Here Futur I comes into play. An assumption is made by using Futur I.
Heute abend wird es wahrscheinlich regnen.
Die VW-Aktien werden wohl in den nächsten Wochen drastisch fallen.
Er ist schon recht alt. Er wird wohl bald in Rente gehen.
In 10 Jahren werde ich genug Geld haben, um mir einen Porsche zu kaufen.
When you talk about plans or you make promises, Futur I is used, too.
Ich werde meine Oma morgen besuchen.
Ich werde mich nächste Woche um die Sache kümmern.
Er wird am Wochenende zu seiner Freundin nach Berlin fahren.
Er wird nächsten Monat nach Asien reisen.
In summary: Not the fact that you’re talking about today, tomorrow or next week is reason for going with present tense. It’s also a question about what you are really expressing. Promises, (perhaps undecided) plans, assumptions are expressed in Futur I, especially when they are less predictable or in the far future. Arrangements, including (decided) plans, are expressed in present tense, especially when they are very predictable and in the near future.
As you probably noticed, some of the examples above can also be expressed by using the other tense. The connotation may change slightly, or not at all. There’s just some degree of overlap where either tense is fine.
In respect to your example, both tenses can be fine and correct. Present tense is more likely, though.
Technically German has a future tense and sometimes it is even used. Not really colloquially, however.
In everyday usage, any type of future unless it’s very distant is described using the present tense. Compare the following examples:
Ich zeig dir gleich was in dem Video. (your example sentence)
Morgen gehen wir wandern.
Nächste Woche habe ich Urlaub.
Nächsten Monat habe ich Zeit für dich.
Ab nächstem Semester werde ich in Braunschweig studieren.
Note how far I went before I considered using werde, the ‘official’ future tense. Of course, one could still mark the studying example with present tense and one could mark the hiking example in future. It’s not strict in any way. However, I would prefer to use the present tense most of the time.