tek, yalnızca, sadece

These words stand for 'only'

I am very confused because I don't know when to use each of them. Can someone please help me with this?

Thank You.

Should I be more specific?

Would someone be so kind to explain me the difference between these words?

Thank You in advance.

Yalnızca and sadece look synonymous to me. I'm trying to think of sentences where they are not interchangeable but I cant think of any. So you could feel free to use any of the two. Sadece looks more common to me. They are both adverbs.

'Tek' has a wider range of meanings. It can be both an adverb or an adjective. Normaly it means "one" or "a single" but it can also mean only.

for instance:
tek ayakkabı
tek kişi
tek adam
This way when it is an adjective it is different than the two.
Also there are a few other cases like these:
tek tek: one by one
tek başına: by himself

Rarely it can be interchangeable with the two above. But it would be better to use it as "bir tek" in this case.

Bir tek seni seviyorum.
Sadece seni seviyorum.
Yalnızca seni seviyorum.
But we say:
Tek sevdiğim kişi sensin.

Dear Erdinc,

thank You very much.

Dear Salukvadze,

Thank You very much. Your explanations are always so helpful to me! You are very kind.
Thank a lot.