Something applied is practical, having to do with real-world situations and problems. Applied physics puts physics into use. If you have a mysterious lump, thank applied physics for the MRI the doctor uses to look inside your body.
To apply is to make use of something, like applying a coat of paint. The past participle, applied describes things related to solving concrete problems, rather than dealing with ideas, principles, or philosophy. Applied chemistry, applied physics, and the applied sciences as a whole have to do with real-world issues. The opposite of applied is theoretical, which is only concerned with ideas.