Hola Colin 

The sentence you saw on the test was this:

Puedes usar mi portátil pero cuídalo bien por favor. 

(You can use my laptop but treat it well please.)

Cuídalo is formed by "cuida" and "lo" meaning "look after it"

Cuidar means "to look after", and here it's using the imperative form of cuidar in the tú form: cuida

It has the object direct pronoun attached to it: "lo" (it, referring to the laptop) 

When we have an imperative affirmative with a pronoun, the pronoun is attached to the verb, so:

cuídalo 

The accent ´ that you see is because now it's a longer word and it is stressed on the antipenultimate syllable, and following accentuation rules it needs the "tilde". 

Here's a lesson about imperatives with pronouns. 

I hope it clarified it. 

Saludos

Inma