Questions & Answers about Materiál dej sem.
Dej is the imperative singular of the verb dát (to give / to put in many contexts).
In this sentence, it means something like put or give as a command:
- dát = to give / to put
- dej! = give! / put!
It is used when speaking to one person informally.
Because dát is the infinitive (to give / to put), while dej is the command form.
Compare:
- dát = to give / to put
- dej = give! / put!
This verb is a bit irregular, so the imperative is not formed in a completely predictable way from the infinitive.