lecken
to lick
To move the tongue over something in order to taste it, eat it, clean it, or moisten it.
Das Kind leckt genüsslich an seiner Eistüte.
The child happily licks his ice cream cone.

to lick / leak
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to lick
To move the tongue over something in order to taste it, eat it, clean it, or moisten it.
Das Kind leckt genüsslich an seiner Eistüte.
The child happily licks his ice cream cone.

The two main meanings differ depending on the subject of the sentence. If a person or animal performs the action, it means 'mit der Zunge berühren' (to touch with the tongue). If an object is the subject, it means 'undicht sein' (to leak/be leaky).
Die Katze leckt ihre Pfote.
The cat licks its paw.
When you move your tongue over something, you use the preposition 'an' with the dative. So you lick 'an' something in German.
Das Mädchen leckte glücklich an seinem Eis.
The girl happily licked her ice cream.
In the meaning 'undicht sein' (to leak/be leaky), 'lecken' (to leak) is used without an object. The subject is the object that something is escaping from.
Das alte Boot leckt und muss repariert werden.
The old boat is leaking and needs to be repaired.
The expression 'jemanden am Arsch lecken können' (roughly: someone can kiss my ass) is very rude and vulgar. It is used only in very informal situations to express strong rejection.
Er sagte, mein Vorschlag sei dumm, aber er kann mich mal.
He said my suggestion was stupid, but he can kiss my ass.
to blow
'blasen' and 'lecken' can both have to do with the mouth, but the action is different. With 'blasen', you move air out of your mouth or with a device. With 'lecken', you use your tongue and move it over something, for example to taste or clean something. The words can be confused because both can occur in physical situations, and 'blasen' can also have a vulgar meaning. In neutral everyday situations, the guide is simple: air belongs with 'blasen', the tongue belongs with 'lecken'.

Das Kind leckt das Eis, damit es nicht auf den Boden tropft.
The child licks the ice cream so it doesn't drip onto the floor.
Bitte blas die Kerzen aus, bevor wir den Kuchen schneiden.
Please blow out the candles before we cut the cake.