How much

Up to you.

For most healthy adults, the Department of Health and Human Services recommends these exercise guidelines:
https://www.mayoclinic.org/healthy-lifestyle/fitness/expert-answers/exercise/faq-20057916

• Aerobic activity. Get at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity a week, or a combination of moderate and vigorous activity. The guidelines suggest that you spread out this exercise during the course of a week. Even small amounts of physical activity are helpful, and accumulated activity throughout the day adds up to provide health benefit.
  
• Strength training. Do strength training exercises for all major muscle groups at least two times a week. Aim to do a single set of each exercise, using a weight or resistance level heavy enough to tire your muscles after about 12 to 15 repetitions

For weight loss it's about calories. Find a way to eat a little less. Exercise isn't going to negate eating too much.

find an exercise or exercises that you can enjoy. Depending on what you want to do with exercise, how much or how little is up to you, there are no set rules.

For weight loss, weights/resistance exercises are king. Building or toning muscle improves weight loss because muscle burns roughly 3 times the calories...the more muscles you work, the bigger or stronger they get and they use up more fuel.