How to: adjsut background & subject seperatey

Hey,

i feel this is a really simple fix, but being new and short on time to Photoshop elements, im needing some guidance. i have some pictures that i need to adjust the lighting and exposer etc. on both the background and the subject. Doing the adjustments to the whole picture isnt getting the result i was looking for. Needing a few straightforward prompts please 🙂