If you're feeling tired or sluggish go for a walk or a jog. Getting blood flowing through your vessels is a great way to wake you up and help with your overall wellbeing. Lifting weights or doing simple body weight exercises (chin ups, push up etc) will also help, however, not as much as cardio!
-It will help you lose weight if you previously did no exercise, whilst maintaining the same calorie intake.
-Mixing in healthy food such as an apple or banana will also help your general wellbeing!
Guides on how to run properly to avoid injury can be found here.
A great website to learn how to lift wights can be found here.