The underdevelopment of the inferior train is a problem which not only occurs with beginners, but with the most experienced people who go to the gym, too.
There are a lot of men who have been going to the gym for years, but who cannot coordinate their legs or just do a few repetitions and that is it.
This happens because the legs are less visible, being covered by pants, but mostly because the training sessions are very exhausting.
The muscle groups in the legs are the ones which sustain you and stimulate your whole body.
You will never be able to maximize your training sessions dedicated to the upper train if you don't have leg muscles which are developed enough.
For instance, the most effective exercise for the development of the back muscles is the bend, not being relevant whether you do this with a dumbbell in your hand or not.
Also, a man with stronger legs or with more developed muscles in that area of his body whose body is sustained by two crayons is rather hilarious, not attractive.
The exercises you do for your leg should start with sessions made of approximately twelve repetitions, therefore, the weights should be proportional to that number.
Once you have done two strength exercises, you can start shaping your quadriceps by doing extensions on the machine.
Don't try to use too heavy weights, but focus more on getting the maximum out of every exercise you do.
This way, your legs will look a lot better.