This simple operation can seem daunting for someone starting out.
Keep in mind there is usually more than one approach to any given process.
This answer probably has things you already know.
Here are s few assumptions about what you already should know first:
A. First, your MIDI keyboard is set up properly
B. You need to know how to zoom in/out of the timeline range.
C. Hovering over an icon will reveal its function name.
D. Adding a new instrument track and assigning an instrument to it:
Menu: Track/Add Instrument Track
Open Browse/Instruments, select an instrument, drag and drop onto track, The instrument editor will appear, choose pre-set. (Clicking the keyboard icon on the track will open/close the instrument editor).
E. Setting Snap functions on the top menu:
Click the "Toggle Snap" button to enable snapping and turn it blue. Under the word "snap", select "Bar". This will snap your location selection to the beginning of a bar when clicking near it.
Process for setting up a loop range of multiple tracks:
1. Selecting a range on the timeline to record:
Move the mouse right above the timeline at the top, it will turn into a pencil, now you can draw a loop range. Draw the range you wish to record in. It is important to have it snap to the bar line. Clicking the "Loop active" button in the transport bar at the bottom or by hitting the "/" key will toggle looping of the range, (selected loop range will turn blue). For now have it not loop - color grey.
Click on the beginning of the time line range in the timeline.
2. Set record functions in the transport bar
In the transport bar, at the bottom, near the word "Metronome":
Click metronome to hear it.
Click Precount to have four precount beats before recording.
Click Auto Punch to record only in the time line range selected.
3. Selecting an instrument track and recording onto it.
Selecting the instrument track puts it into record mode (record enable button turns red).
4. Start recording
On the Transport panel at the bottom, click "Record" or hit NumPad(*)
Record notes with your keyboard, it will stop recording at the end of the loop range.
Set it to loop ("/") and play back to hear how it sounds looping.
5. Add new tracks and record them as needed using the same range but turn off looping while recording. Turn on looping while playing back.
6. When done, turn off looping and, using the Arrow tool on the top left, select all the recorded ranges, (they should all have the same start and end points). Hit the "D" key on the keyboard to duplicate them back to back, multiple times if needed.
7. With this "looping" of those recorded tracks you can now add additional tracks and record them as needed along with the loop.
(Editing tracks: fixing notes is another topic)