i have a problem with my lasso tool i was watching a tutorial and making my first project (i'm new), and I've encountered this problem, my lasso tool keeps getting messed up and i don't know how to fix it, it is supposed that when i select something the tool looks like a square 


but it looks like this when i try to use it 


.

please help me as i am new to blender and its really bugging me how its changing every time
, i am not sure if i have pressed any button which is a shortcut to change a setting or something like that.

thank you.
The selection tool can be changed by


locating the tool bar in the top-left of the 3D Viewport (T if it is hidden)
long pressing on the selection tool icon (usually the arrow with the selection tool)
choosing the proper selection tool from the appearing menu