made an extra windo but cant get rid of it

I accidentally pulled down from the top which got rid of my top toolbar and added a new perspective window (or what ever it is called) and i keep trying to use the little triangles in the corner but all that does is make another window (but i can get rid of these). Also because of this window i can no longer change to any other mode apart from object mode.

RMB on the border between the 2 windows and select Join, drag your mouse to select the direction you want to join

If using the triangle method, drag into an adjoining window to join them

Also because of this window i can no longer change to any other mode apart from object mode.
Don’t understand this