Go for a Walk or a Run
This is better done outside so that you can connect with nature but running inside on a treadmill is almost as good. You can time yourself and increase length and time according to your fitness program.
Always have new goals to reach. Start with brisk walking and work up to running. At my age, I am still walking!
The health benefits are considerable. You can build stronger bones and you can help to maintain your weight.
Also, you are helping your heart to stay healthy and keeping your blood pressure low.
Jumping Jacks

Michelle Obama is a great fan of this exercise and has become “Jumper in Chief.” They are great for cardiovascular health and also for toning muscles especially the calves and the deltoids.
Stand with feet together. Jump while spreading your arms and legs. Return to first position and keep going! You can start with doing these for 1 minute and then gradually build up to the number you are comfortable with.
Leg Squats

Not just legs are involved but also hips and knees.
Stand with your feet a bit further out from your hips. Arms are out in front of you. Then lower yourself as if you wanted to sit down until you reach a 90 degree angle. You can go down further if you want to. Then return to the starting position. Repeat 15 times for 2 sets for beginners.
Push Ups

You start lying down (face down) but with your body held up at arm’s length. Your hands should be in line with your shoulders. Breathe in as you lower your body. That is fairly easy. Now, as you exhale, you have to get back up to the starting position.
An easier version to start with is to bend your legs at the knees so you do not have to lift your whole body.
Bicycle Crunches

There are numerous crunch exercises targeting the abs. The bicycle crunch is a variation where you work more muscle groups. Aim for 15 to 20 reps to start off with.