Me gusta la fruta  I like fruit

¿Te gusta la sandía?
Do you like watermelon?

Sí, me gusta.  /  No, no me gusta.

¿Te gustan las uvas?
Do you like grapes?

Sí, me gustan.  / No, no me gustan.

In English, you say I like things.  In Spanish, you say me gusta the thing.

Or we can say the opposite, no me gusta.

So you can say, 

If you're talking about more than one thing, add the letter "n" to the word "gusta":

Notice how you say you like something or don't like something:
 English  Spanish
 I like it Me gusta 
I don't like it  No me gusta 

Then how you say that you like some things or don't like some things:

Notice how you say you like something or don't like something:
 English  Spanish
 I like them Me gustan 
 I don't like them No me gustan 

Then how to ask if someone likes something or things:
 English  Spanish
Do you like it? ¿Te gusta?
Don't you like it?
¿No te gusta?
 Don't you like them? ¿Te gustan?
 Don't you like them? ¿No te gustan?

Then how to ask if someone who's not there likes something or some things:
 English  Spanish
 Does he / she like it? ¿Le gusta?
Doesn't he / she like it?
¿No le gusta?
 Does he / she like them? ¿Le gustan?
 Doesn't he / she likes them? ¿No le gustan?

If you're at a restaurant, the waiter or waitress may ask you if you would like something - te gustaría -, and you can answer that you would like it, please - me gustaría.

¿Te gustaría una ensalada de fruta?
Would you like a fruit salad?

Sí, me gustaría una ensalada de fruta.
Yes, I'd like a fruit salad.

Here's a video from Plaza Sésamo, the Mexican version of Sesame Street, about the importance of eating fruit: