What does multi kick mean in magic the gathering?

Answer 1

Multikicker is an additional cost, and functionally it is just like the regular Kicker mechanic, but you may pay it multiple times. The exact cost and effect of a specific Multikicker is listed on the card itself, as it can differ from card to card.

So take 'Comet Storm' which costs XRR, and has a Multikicker of 1. You could have X as 2, and Multikick it twice, meaning you pay 2, RR, and another 2 as an additional cost. Comet Storm's multikicker says "Choose target creature or player, then choose another target creature or player for each time Comet Storm was kicked. Comet Storm then deals X damage to each of them." so you pick three targets in total, and Comet Storm deals 2 damage to each of them.

Answer 2

'Multikick' is an additional cost that can be paid when casting the spell, and this cost can be paid multiple times. Bloodhusk Ritualist is a 2/2 Vampire Shaman who costs (2)(B) and has a multikicker of (B). His effect says when he comes into play, target opponent discards as many cards as he was kicked.

So, if you want them to discard two cards, you will announce you are casting Bloodhusk Ritualist, and kicking him twice. That means you need to pay (2)BBB in total. When he comes into play, his effect will trigger and make target opponent discard two cards.