Introduction:

Contractions are used in informal speech. English will not distinguish on occasion between similarly spelt contractions so that they have to be comprehended through deduction.

Consider you’d
You’d be better of if you visited the client. (in this case ‘d is a contracted for of would).
You’d seen the client several times. (in this case ‘d is a contracted form of had)
You’d better see the client. (in this case ‘d is a contracted for of had)
You’d (had) a great time on the trip. (less common but still used in spoken English - in this case ‘d is contracted for of had)

Structure:

Contractions a mostly used with personal pronouns but in informal speech they can be used with nouns.
Jane had thought it was over.
Jane’d thought it was over. (Informal but commonly used in spoken English)

Examples:

I’d like to see Jack.
It’ll be a while before they finish.