信心(xìn xīn) - confidence, faith (in something) in Mandarin

信心 (xìn xīn) is confidence in the sense of belief that something will go well: in a person, a plan, a team, an outcome. It is a thing you have, gain, lose or build, so it lives with 有, 没有, 失去 and 增强.

The frame to learn is 对 ... 有信心. The thing you believe in goes after 对, not after 信心: 我对你很有信心. English lets you say confidence in you; Mandarin marks the target first and the possession second.

The trap is confidence as a personality trait, which is 自信, not 信心. 他很自信 describes a self-assured person; 他很有信心 says he believes this particular thing will work out. Get the two swapped and you will accidentally call a nervous colleague arrogant.