la
la is a particle of toki pona used to separate a sentence from its context.
Functions of la
la is a context particle. Anything that comes before la in a sentence is taken as context for the rest of the sentence. "X la Y" –> "in the context of X, Y." Everything besides this is just an extension/different version of this.
ma mi la kon li lete = "In the context of my land, the air is cold"
It can be used to convey the same information as lon. Anything that you would say after a prepositional lon, you could put before a la and it would mean the same thing.
mi pilin pona lon tenpo ni == tenpo ni la mi pilin pona
jan mute li lon ma ni == ma ni la jan mute li lon
It can also move other prepositional phrases to the front, often negating the need for the preposition (but not always).
ni li pona tawa mi == mi la ni li pona
sina pali e ni tan seme == tan seme la sina pali e ni
A la-phrase can even take entire sentences under it, making a conditional phrase
suno li loje la tenpo li pona = "When the sun is red, the time is right"
sina weka la mi pilin ike = "If you leave, I'll feel sad"
It can also form conjunction-like phrases with single words.
ni la ≈ "so/then"
ante la ≈ "in any case/anyway"