Window selection and Delete.
If you want to select the lines created click the bottom right corner of the canvas and then again in the top left, (then from right to left).
Doing so will create a "selection window" within which you must include all or part of the lines to select.
You can also make the window by clicking first on top and then down and from left to right, but be careful, in this last case is different because it will select only objects that are entirely within the window.
In later versions of AutoCAD this selection box is colored in, respectively, green or blue, just to highlight the difference.
Done this the lines are selected (become slightly highlighted and blue squares appear at the top and center), now press the "Del" key on the keyboard or the delete key on the modify toolbar.
You can also do the reverse, first activate the command "delete" button on the toolbar, then click the selection box and press "enter" to cancel.
Make some tests of controls that have been described, (line, offset, window selection and delete).