Ok i was assembling the fork and handle bars but i ran into a problem with the fork. There are no threads on the collar of the fork and so i dont know how to keep it from sliding out of the frame. could someone help me with this please thanks

Is this a new fork for an old bike? Perhaps you got a threadless fork-- pretty much all modern forks are-- and the stem is for threaded forks. Threadless stems simply clamp onto the steerer tube of the fork and that's how the whole thing stays assembled.

Chuckie

Some kind of Voodoo? bk

as with matching parts. Did you place the 2 forks back to back and match it?

your fork may be to short or as mentioned no threads means you now have a threadless fork and need to change the headset and stem to match it.

https://www.parktool.com/repair/readhowto.asp?id=65

https://www.parktool.com/repair/readhowto.asp?id=127

These sites will show you the difference between threadless and threaded forks.