How can I sell my songs/poetry if I haven't made melodies for them?

Depends on the market they are geared too. The two genres that use lyrics other folks write most heavily are Pop and Country. If the lyrics you are writing are more geared for Rock then your best bet is to find a composer or a singer who needs lyrics and tie your horses to their success. With them you don't sell it outright instead you get a share of the royalties garnered by the song. In both cases the more successful your lyrics are the easier it is to make a living writing them, though very few people manage that.

If your serious about your effort there are some good groups on Yahoo and Google to get critque. Your also welcome to send me a copy of some but expect brutal and honest critque. To hone your craft you need good feedback. The only way your going to get better is to get that kind of feedback.

On the flip side remember feedback is just ONE view on it. Unless you get the same thing from multiple people then you need to take it under consideration but just because I or anybody else says something doesn't make it necessarily so. When it comes to poetry and lyrics there is no hard right or wrongs. It's an artisitic endeavor like music. Everybody will have different tastes and you need to take them under consideration and choose the advice you feel is most helpful.

im sure you do not have to have melodies for your songs or poetry

because sometimes the song or poetry have move meaning (especially poetry)