No 'Select' option in Photos app on macOS High Sierra

iPhones have a select mode chosen by the "Select" button. Since Macs have keyboards and trackpads, they don't need the Select mode. When you click on a single picture, it's selected. As léonie says, you can select multiple pictures by command-clicking each in turn. In a line of pictures you click on the first and then shift-click on the last to get all the in-between pictures. It is because iPhones don't have a shift-click or a command-click that they must have a special "Select" button.

You might want to look at this:

Select items on your Mac screen - Apple Support

Have you tried to click one photo, then hold down the command key ⌘ and click further photos to select more photos?

Which view are you in, when you try to select and delete photos? Are you viewing All Photos? Or are an album or smart album or a shared album? Or a project?

If the two command keys ⌘ to the left and right of the space bar are not working, you will be having a hard time to work in Photos. Consider to replace the keyboard by model that is working with your Mac.

But to select a range of multiple photos you can also try to click the first photo of the range, then hold down the Shift key ⇧ and click the last photo of the range.