Did you like it?

Bonjour Emma,

Ça t'a plu?  --> Ça is a pronoun meaning "it / that" in this context.

Tu (Subject pronoun, second person singular) reduced to t' in front of a (avoir) and a plu is the verb plaire (to please) in the passé composé.

So we have the query  Ça t'a plu? --> Did you enjoy that? In question format, and it would have been asked with a raised intonation.

Bonne continuation

JIm

Emma, 

not sure exactly what it is you are asking for clarification on? 

Jim has covered the construction of ‘ plaire ‘ in passé composé, but if you are also asking about the grammar more generally - see the lesson linked here :

 Expressing you like something/someone in French with the verb "plaire"

‘ Plaire ‘ is one of the verbs that seems to ‘ work in reverse ‘ from an English speaker’s perspective. The verb ‘ manquer ‘,  used in an emotional context is another, so worth looking at both lessons together. 

 Using manquer (à) to say you miss someone or something emotionally in French

It's the t'a that i dont understand. I would have written it Ça, tu a plu? Is the 'tu a' just simplified to 't'a'?

Emma, 

This is elison - it is a formal elision and is compulsory in speech and in writing.

The sentence is  ' Ça t'a plu ' - there is no comma here as it is simply the standard ' subject-object pronoun-verb ' construct.

Ça is the subject so the conjugation of avoir is ' a plu ', as Jim notes. 

' te ' is the indirect object pronoun (it is not the subject pronoun ' tu ' ), and this compulsorily elides with ' a (plu) ' to form " t'a (plu) ". 

 https://french.kwiziq.com/revision/glossary/contraction/l-elision-elision

 https://www.lawlessfrench.com/pronunciation/elision/

Maarten is quite correct.

" te is the indirect object pronoun (it is not the subject pronoun ' tu ' ), and this compulsorily elides with ' a (plu) ' to form " t'a (plu) ". 

Plaire takes an indirect object and in this case the pronoun te.

Jim

Just to chime in at the end:

Ça t'a plu -- You liked that.

This sentence has the roles of subject and object reversed in English. In French, ça is the subject and te (t') the object. In English, it's the other way around: "you" is the subject and "that" is the object. You can get a feeling for the French by using "pleases" instead of like:

Ça t'a plu. -- That pleased you.