Baselines are normally created by your UCM project administrator. If the resources in the asset that you want to submit do not exist in the baselines that your stream is configured for ask your UCM project administrator to create one for you.
The stream that you are using must be configured to use the baseline that contains the file artifacts of the asset that you want to submit.
The versions of the file artifacts in your workspace must be the same versions on the baseline. This could include files that are checked out, or that have been checked in since the snapshot view was created.
You begin with a pristine view that contains the artifacts and files that you want to have in your asset. Then you create the asset in the Asset Editor and add content that is under source control.