Breakdown of Ich komme morgen. — Das macht nichts.
ich
I
kommen
to come
morgen
tomorrow
Das macht nichts
it doesn't matter, never mind
Questions & Answers about Ich komme morgen. — Das macht nichts.
Why does it say Ich komme (I come) instead of using a future tense like 'I will come'?
In German, it is very common to use the present tense to talk about the future, as long as there is a time word that makes the context clear. Here, the word morgen (tomorrow) tells us this is happening in the future, so the present tense Ich komme is all you need.
Why is morgen written with a lowercase letter here? Aren't German nouns always capitalized?
You are exactly right that German nouns are capitalized! When capitalized, der Morgen is a noun meaning 'the morning'. But when written with a lowercase letter, morgen is a time word (an adverb) that means 'tomorrow'.
How does Das macht nichts translate to 'It doesn't matter'?
This is a very common fixed expression. Literally, it translates to 'That makes nothing' or 'That does nothing'. Germans use this exact phrase all the time to say 'It doesn't matter', 'No worries', or 'Never mind'.
Could I just say Das macht nicht instead of Das macht nichts?
No, you need the 's' at the end. The word nicht just means 'not', which would leave the sentence incomplete. The word nichts means 'nothing'. The phrase specifically uses nichts to say 'That makes nothing'.