First get the ~ます masu form of the verb you want to do. Then drop the ~ます masu and add ~たい tai.
| たべます tabemasu (to eat) |
|
たべ tabe |
|
たべたい tabetai (want to eat) |
| のみます nomimasu (to drink) |
|
のみ nomi |
|
のみたい nomitai (want to drink) |
| します shimasu (to do) |
|
し shi |
|
したい shitai (want to do) |
Of course if you want to say "do you want to..." Just add ka
ケーキ を たべたい です か?
ke-ki o tabetai desu ka?
Do you want to eat cake?