claim head of household & I have 2 dependents, one that qualifies for the child tax credit. what to put for the amount/% to “withhold” for federal taxes to be withheld

So far federal taxes have not been withheld from my paycheck and I’m not sure why? I believe with this new form for tipped employees. We have to write the amount we want to have withheld or the percentage and I have no idea how to figure that out it makes no sense to me.