adverb
tomorrow, in the morning (depending on capitalization)
A1
morgen: as lowercase adverb means 'tomorrow' (temporal). Capitalized 'Morgen' is a noun meaning 'morning'. Use with verbs to indicate future actions (Wir sehen uns morgen). No specific preposition required. Common in spoken and written German; collocates with times (morgen früh, morgen Abend).
Examples
Morgen wird das Wetter besser sein.
Tomorrow the weather will be better.
Ich gehe morgen ins Kino.
I'm going to the cinema tomorrow.
Der Veranstalter kündigte an, dass das Konzert morgen beginnen würde, obwohl noch Karten übrig waren.
The organizer announced that the concert would start tomorrow, although tickets were still available.
Details
Mnemonics
Picture a sunrise with the label 'morgen' indicating the next day.
Same root as English 'morrow' (tomorrow).
Notes
Lowercase 'morgen' = 'tomorrow' (adverb). Capitalized 'Morgen' is the noun 'morning'.