New - Help - select cells + Free Tutor

Just started learning Excel have 9 hour in so far and practing today not in
class I could not select cells... I got the + on the right bottom corner but
when I dragged it down with numbers in the cell it copied the 123 numbers in
the first cell and over wrote the 2 and 3 rd cell when I dragged with shift
it numbered the cells 123 124 125 when I dragged with ctl it made 2 cells
blank and pasted my numbers below does anyone know what I did wrong or what
setting I need to change on my home computer to get it to work like the one
in class ?

thanks

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