You can find both the Commands quick reference (straight list of commands and keys) and the User Guide (has more detail) from NVDA's help menu.  Press NVDA+n to open the NVDA menu, then H for help.  The NVDA key will be either INSERT or CAPS LOCK, depending on how you set it up.

As you are coming from Jaws, another document you might be interested in, is the guide to Switching from Jaws to NVDA, which you can find here: https://github.com/nvaccess/nvda-community/wiki/SwitchingFromJawsToNVDA

As for your specific question, in Desktop keyboard layout, NVDA uses NVDA+up arrow to read the current line, but that is the up arrow key itself, not the 8 on the number pad.  Note that you can set the NVDA modifier key and whether NVDA uses desktop or laptop keyboard layout independently of each other).  In laptop keyboard layout, the keystroke to read the current line is NVDA+L.  Similarly the keystroke to read from the current point onwards is NVDA+down arrow in desktop keyboard layout and NVDA+A in laptop keyboard layout.

If you are interested in learning NVDA from scratch, we do have "Basic Training for NVDA" available.  You might find that you do already know a lot of it, so work through the switching from Jaws to NVDA guide first and see how you feel after that.  If you are interested in Basic Training for NVDA, it is available from our shop: https://www.nvaccess.org/shop/

Kind regards

Quentin.