Now why the code below adds 1 for it to move or someting
Ummm... it's hard to be sure, but it sounds a bit like you just need the way the display works explaining. x% is used to hold a coordinate for the text's position on the x axis. To put text on the extreme left of the screen you'd type...
Text 0,20, "Hello World"
...and to put it on the extreme right you'd use...
Text 799,20, "Hello World"
...which is why increasing the value of x% places the text further and further right each loop. The second value, 20 in the above examples, is used to determine how far down the screen the text is drawn. So, to put those two things together, you could place text at the top left of the screen with...
Text 0,0, "Hello World"
...and at the bottom right with...
Text 799,599, "Hello World"
Sorry if you already know this, but it's the answer to the only question I can see in the original post.