Learn Polish: Dam radę, nie martw się. - I'll manage, don't worry.

Dać radę is one of the most common idioms in Polish. While it literally translates to "to give advice", it is almost always used to mean "to manage", "to cope", or "to handle something". Because you are saying "I will manage", you use the future tense form dam (from the perfective verb dać).

Why is the word for advice written as radę instead of rada?

It is the direct object of the verb dać (to give), so it must take the accusative case. For feminine nouns ending in -a like rada, the accusative case changes the -a ending to -ę.

How is the command form martw created from the verb martwić się (to worry)?

To form the imperative (command) for a single person, you usually look at the present tense "they" form, which is martwią się. By dropping the ending, you are left with the core stem martw.

I have learned that the reflexive pronoun się shouldn't be the last word in a sentence. Why is it at the end here?