How to open folder without using mouse in Mac?

To open it, use ⌘+O (or use the alternative ⌘+↑).

I use Command plus the ↑ or ↓ arrow keys.

As well, you can also use Command+Shift+G while Finder is active and type the path of the folder you want to open in the box that appears. ie:

~/Pictures

will open your Pictures folder.