It is to be noted that in this Photoshop exercise, the technique used was to fill and switched the contents to color and turned to the color red. It is to be noted that this is not the only technique for achieving the above results.
To make a rectangle selection, utilize the rectangle Marquee Tool. To make a circle selection, use the Elliptical Marquee Tool.
To choose a single row of pixels, use the Single Row Marquee Tool. The Single Column Marquee Tool is used to pick a single pixel column.
Note that the marquee tools are excellent for picking geometric forms, while the lasso tools are excellent for creating more free - form designs.
Of course,you can use any of these tools in conjunction with one another to create more complicated shapes at any moment.