Basic selections are a necessary knowledge if you plan on getting better with photoshop. A basic selection is used for isolating(selecting) different areas of the image.
A good knowledge of this will allow you to create much better edits by allowing you to apply adjustments to specific parts of the image rather than the whole thing. There are two basic selections tools, the Marquee and the Lasso tools. They both have few different variations as follows
With the marquee tool, your first click will set the beginning of the selection. From there, drag until you have everything you want selected and let go wherever you would like the selection to end.
For the standard lasso tool, simply hold the mouse down and draw your selection in. With the polygonal tool, click once on a spot, and click again to create a line. create shapes with the lines by clicking different points, and then finally click on your first point to complete the selection. And finally, with the magnetic tool, follow the edge of something in your image and the lasso will automatically “stick” to that edge and help you make a fine-tuned selection.
You can also add or subtract from selections by using the advanced selection options or keyboard shortcuts.
Get your hands on some of the basic tools and start experimenting. Selections are important and will drastically improve your editing abilities!