This is the 6673rd most frequent Turkish word.
be
The Turkish word "be" is an informal expression used to grab attention, emphasize a point, or express frustration, similar to "hey" or "man" in English.
Here, 'be' is implicit as the verb 'im' indicates the state of being cheerful.
Ben neşeliyim.
I am cheerful.
In this sentence, 'ol' acts as 'be,' used to indicate a state or action to be happy.
Kutlama başladı; eğlen, mutlu ol, ve kutlama sonra bitmesin.
The celebration began; enjoy, be happy, and may the celebration not end.
'Ol' in this instance again represents 'be,' but reflects an imperative mood to advise being true to oneself.