Mix the cards up well, please.
Why did you mix one woman into group with a bunch of men?
It’s dangerous to mix tofu and puffer fish.
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means mix so the verb version is to mix.
There are similar words to this one, including 交じる which means "to be mixed" and 交わる which means "to intersect." This one is when you're doing the mixing. Like 交じる, the connotation is that the things being mixed are distinguishable from each other, like two types of fish, or books being mixed together. They don't become homogenous like paint or something would.
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You have to remember the ま portion. Who would mix things for you (like cakes and other goodies) growing up? That would be your Ma (ま).