How can I set my upload path by date?
First you create an asset source uploads. Then you create an asset field and set its upload location subfolder to {postDate|date('Y')}/{postDate|date('m')}

When you edit an entry, any files you upload will go in the subfolder for the year and date. If you have selected Restrict uploads to a single folder? in the asset field, then only assets in that subfolder can be used.