This is the 276th most frequent Tamil word.
கவ
The Tamil word "கவ" means "to protect" or "to guard."
Here, 'கவல்' (kaval) is a root word representing 'concern'; in this imperative usage, it has become part of a phrase reassuring the listener.
கவலை வேண்டாம்.
Don't worry.
In this sentence, 'கவனம்' (kavanam) indicates 'attention' or 'focus', and it is used to describe an action.
அவன் கவனம் செலுத்துகிறான்.
He is paying attention.
'கவனமாக' (kavanamāga) is an adverb form meaning 'carefully', modifying the verb to specify the manner of observation.