first try

[Furansujin]

I want to say:

I like to smoke cigarettes, but I want to stop.

Is this right ? (not sure of sentence construction and vocabulary)

煙草は煙ますが好きですでも, 止ますがほしいです．
tabako wa kemumasu ga seki desu demo, tomasu ga hoshii desu.

Is it well "とまる" -> "とます" to say stop something ?

It is one of my first sentence, maybe wrong but happy to try!

[adam]

It would be,

タバコを吸うのがすきですけど、やめたいんです。
tabako o suu no ga suki desu kedo, yametain desu.

[Furansujin]

Arf! I was far from the right sentence!! Just がすきです right! (more than nothing:()

What is "kedo" and why don't use "demo", I can't find it in grammar lessons?

Use "wa" instead of "o" was really a bad mistake, I want to go faster than I can!
Thanks for the right sentence, I learn from my mistakes!

[richvh]

"Demo" can only be used at the start of a sentence, whereas "kedo" can be used to join clauses.

[Furansujin]

ok thanks.
Just a last question. In the -tai form of やめる, why do you add a ん?
やめたい without ん is wrong?

Thank you very much to all for your help!

[richvh]

-n-desu (or, more fully, -no-desu) gives an explanation. See Tae Kim's explanation or Matt Kammermans' explanation

[Furansujin]

Ok that site is great. thanks Richvh

[Shibakoen]

For the last part, could you use 「禁煙」 like 「禁煙したい」 or 「きんえんしなきゃ~」?