/prAdi / प्रादि

The /prAdi are, in alphabetical order:
/adhi /abhi /AG /anu
/ati /apa api /ava
dur /dus /ni nir /nis
/pari /pra /parA /prati
/sam /su' upa /ut /vi.

By upasargAHkr..., these are called /upasarga when before a verb.

These /prAdi are like the little words "up, for, on, with" that appear in English in expressions like "eat up", "look for", "look down on", "put up with". They are the ones you are not supposed to end English sentences with.

In Sanskrit you ACTUALLY don't ever end sentences with these. They always come right before a verb, or right before something else.

Like in English, adding one of these to a verb can change the meaning predictably, —

IkSate "looks"
/vi + IkSate → vIkSate "looks all around", "commands a view of"

or randomly, —

gacchati "goes"
avagacchati "understands"

padyate "steps"
prapadyate "undergoes"

or not at all —

viveza "went in"
praviveza "went in"

Why didn't you mention that English grammarians call things like "up" "prepositions"?

Because that's a misnomer. They are positioned AFTER the English verb, not previous to it. Preposterous. Just thinking about that causes grinding of teeth and squeejing of neurons.

Well, they why don't you call their Sankrit cousins like /upa "prepositions"? They go before the verb in Sanskrit, after all.

Because I sort of like how /upasarga and /prAdi sound. Those words make me think of pastries for some reason.