conjunction
the more ... the more
B1
Desto is part of the correlative comparative pair 'je ... desto ...' meaning 'the more ... the more'. It links two comparative clauses: the first uses 'je' and the second 'desto'. It’s not a preposition or verb; word order follows dependent-clause rules in German.
Examples
Je länger das Projekt dauerte, desto schwieriger wurden die Entscheidungen, weil das Team weniger Ressourcen hatte.
The longer the project lasted, the more difficult the decisions became, because the team had fewer resources.
Je mehr er übt, desto besser wird er.
The more he practices, the better he gets.
Details
Mnemonics
imagine two rising bars: 'je mehr' (first) and 'desto mehr' (second) to link cause and effect
pair with 'je ... desto' — think 'desto' = 'the more' in English
Notes
'desto' is used in the correlative construction 'je ... desto ...' (the more ... the more ...). It cannot stand alone; usually appears in the second clause.