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 squeeze, so the verb version is to squeeze. The way that this word differs from 絞る is that the former means "to wring out" and the latter means to squeeze or to juice fruits/vegetables or to milk a cow.

Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You haven't learned this reading yet, so here's a mnemonic to help you:

After the farmer milks the cow, she bows (しぼ) to the cow to say thank you for letting her squeeze out some fresh milk.