to enjoy oneself
Building blocks
lõbu- - fun
-tse- - ongoing activity (continuative)
-ma - infinitive ending
Possibly it’s derived from: lebama, which means to lie down. There is also a word in Finnish: lepo, which means to rest.
Another possibility is that it’s derived from Proto-Germanic: slēpaz (to sleep)
Looking at where the word lõbu is likely derived from it’s clear that having fun and resting/sleeping go hand-in-hand.
How to use it
Lõbutsema is a so-called intransitive verb, meaning it doesn’t take an object.
You can just “have fun” but you cannot “have fun something”.
Like with all other verbs, the person doing the action (i.e. the fun-haver) is indicated by the Nominative case (1st base form).
Examples
Eile lõbutsesin lastega mänguväljakul
Literally: “Yesterday had fun with children on playground”
Idiomatically: “Yesterday I had fun on the playground with children”
Eile - Adverb - "Yesterday"
lõbutsesin - Verb - 1P Past Sg, "I had fun"
lastega - Noun - Comitative Pl, "with children"
mänguväljakul - Noun - Adessive Sg, "on the playground"Lõbutse tänasel peol!
Literally: “Have fun on today’s party!”
Idiomatically: “Have fun at today’s party!”
Lõbutse - Verb - Imperative mood 2P Present Sg, "Have fun"
tänasel - Adjective - Adessive Sg, "on today's"
peol - Noun - Adessive Sg, "party"