How can I draw a new single vertex? I´m trying to make these boots and I need to draw this opening on the front but I don´t have the vertex in the way I needed to. How can I create those new vertex? Thanks!
You can use the knife tool K to draw a gap.  Then you can do it with two different ways.

Just manually delete the the faces you drew and fill the inside.
Or you can use default add-on named loop tool. You can enable it in preference section. Just select the top and bottom face and apply bridge in loop tool.
Hope that helps.