When you want to grab a creature or wrestle with it, you can use the
Attack action to make a special melee attack, a grapple. If you’re
able to make multiple attacks with the Attack action, this attack
replaces one of them. (PHB p.195)
For example, if you have a 5th level Champion, you can try to grapple your opponent, and if you succeed with the grapple attempt then the second attack (with a weapon like a war hammer that you have in your other hand) is available. Note that you can't now have a shield unless you have a third hand, and it has to be a weapon you use one handed.
Using at least one free hand, you try to seize the target by making a
grapple check, a Strength (Athletics) check contested by the target’s
Strength (Athletics) or Dexterity (Acrobatics) check (the target
chooses the ability to use). If you succeed, *you subject the target
to the *grappled condition** (see appendix A).
The condition remains until it ends. The target is grappled until either it escapes the grapple (which requires the target to use an action) or you voluntarily release the grapple.
• A grappled creature’s speed becomes 0, and it can’t benefit from any bonus to its speed.
• The condition ends if the grappler is incapacitated (see the condition).
• The condition also ends if an effect removes the grappled creature from the reach of the grappler or grappling effect, such as when a creature is hurled away by the thunderwave spell. (PHB Appendix A, Conditions)
Hold 'em by the arm and smack them in the head with your hammer, for as long as the target is unable to get free of you.
From your comment:
So I can't use my legs to (for argument's sake) lock over the shoulder
and under the arm and strike with 2 daggers using the dual wielder
No, you need to use at least one free hand per the rules. If you want to use cool judo moves, or cool wrestling moved, you'll need a DM ruling for that. As to your picture, the feet wrapped around the waist of the target don't matter, per the rules.