If you want to say in German that you like something, there are many different expressions that I’m going to explain in this post (the first of two).
1. gefallen (irregular: gefällt; hat gefallen)
a) Grammatical structure
The thing you like (e.g. the song, the car, the shirt …) is the subject (nominative). Consequently, it conjugates the verb: If it’s just one thing you like, you have to use the 3rd person singular (gefällt) and if it’s more than one thing, you have to use the 3rd plural (gefallen).
The person who likes the thing(s) mentioned is in dative case (mir, dir, ihm, etc.). This is exactly the same grammatical structure as the Spanish “me gusta(n)” or the Italian “mi piace (piaciono)”.
Examples:
Das Lied (subject) gefällt mir (dative object). (I like the song.)
Die Lieder gefallen dir. (You like the songs.)
Gefällt ihm das T-Shirt? (Does he like the T-shirt?)
It’s very usual and also correct to swap the subject’s (1st) and the dative object’s (3rd) position:
Mir gefällt das Lied.
Dir gefallen die Lieder.
b) Use
This verb is used mainly with things (except for food/drinks), never with verbs! You can also use it for people meaning that you like them (can express both personal attraction and/or that you find them nice/cool).
2. mögen (modal verb: mag, magst, mag, mögen, mögt, mögen; habe gemocht)
a) Grammatical structure
You (the person who likes something) are the subject and, thus, conjugate the verb. The thing you like is the accusative object. This works just like the English “I like”.
Examples:
Ich (subject) mag das Lied (accusative object).
Du magst die Lieder.
Mag er das T-Shirt?
b) Use
Mögen is a synonym for gefallen (neither used with verbs) but you can use it for food and drinks.
When talking about people, it has also the same meanings as gefallen but when referring to personal attraction it can shift towards a more intense feeling (ich mag ihn sehr = I like him very much, he means a lot to me).
3. gut finden (du findest, er findet; habe gefunden)
This verbal expression answers the question: Wie findest du …? (How do you find/like …?)
a) Grammatical structure
Grammatically, finden works just like mögen but you have to add gut at the end.
Examples:
Ich finde das Lied gut.
Du findest die Lieder gut.
Findet er das T-Shirt gut?
b) Use
Exactly the same as gefallen.
Negation
You put nicht/kein after the verb (but before the adjective). Use nicht if there is no noun, use kein if there is a noun and you put the negation before it:
“I don’t like this.”
Das gefällt mir nicht. / Mir gefällt das nicht.
Ich mag das nicht. / Das mag ich nicht.
Ich finde das nicht gut. / Das finde ich nicht gut.
“I don’t like red cars.”
Mir gefallen keine roten Autos.
Rote Autos gefallen mir nicht. / Mir gefallen rote Autos nicht.
Ich mag keine roten Autos.
Rote Autos mag ich nicht. / Ich mag rote Autos nicht.
Ich finde rote Autos nicht gut. / Rote Autos finde ich nicht gut.
In the second post about “How to say to like in German” you can find exercises about this topic.