I want to have a box with a single line on the left of the box with the possibility to change color and thickness. Something like that : .
If it's possible with the tikz package, i would like to know with with commands
yes, this is possible with tikz. Since some users wanted something like that, Thomas F. Sturm developed the tcolorbox package, which gives you a quite simple interface to achieve that.
The smart way: Calm down and take a deep breath, read posts and provided links attentively, try to understand and ask if necessary.