How do I get my Macbook Pro back to normal and keep all my files when I'm in "macOS Recovery"? My "Notes" app was non-responsive and lagging so I manually shut down my MacBook Pro by pressing down the off button for several seconds (It's from 2013 or older and I think I have OS X Mavericks or maybe a newer operating system). When I turned it back on it was in "macOS Recovery" mode. How do I get it back to normal and keep all my files and everything?
There are a few things you can try.

1. Use the SDM to try booting from your usual Startup Disk

Use Startup Disk Manager to see if your usual startup disk is available. Follow these steps:


Shut down your MBP
Switch it on and immediately press and hold the option key
Release the key when your bootable disks start appearing
If you see your usual startup disk, try booting from it


2. Try running Disk Utility from macOS Recovery


Boot into macOS Recovery
When the macOS Utilities window appears, select the Disk Utility option
Check to see if Disk Utility can see your usual startup disk
If so, use Disk Utility to repair your startup disk
Assuming it completes okay, try again to boot up your MBP


3. Run Apple Hardware Test or Apple Diagnostics

It's unclear from your question the exact model of MBP you have, so it's not clear whether your Mac used Apple Hardware Test or Apple Diagnostics (Apple switched to the latter in June 2013)

While the process of using these is slightly different, how to access them is the same:


Shut down your MacBook Pro 
Restart your MacBook Pro
Press and hold the D key before the gray startup screen appears
Wait for either AHT or AD to load


If it's AD it'll automatically run the diagnostics - just wait for it to finish and report back
If it's AHT, select your language and click the right arrow to access your test options. I suggest you select the "Perform extended testing" checkbox before you click the Test button.



Assuming this finds no hardware problems, it may be time to consider reinstalling macOS.

4. Reinstalling macOS without deleting applications, data, etc

Prior to following this process, you need to ensure:


you have a known good backup of all your data (be it via Time Machine or another process) just in case something goes wrong
your MacBook Pro is able to connect to the internet during the installation process
you have already confirmed that your usual startup disk can be seen by Disk Utility (see 2 above) and that the repair process itself completed without problems


Assuming you have the above sorted, follow these steps to reinstall macOS without deleting your apps, data, etc.


Shutdown your MBP
Power up your MBP and immediately press and hold the commandR keys
Let go of the keys when it's clear you're booting into Recovery mode
Soon the macOS Utilities window will appear
Make sure your iMac is connected to the internet
Now choose the Reinstall macOS option 
Click the Continue button
Follow the prompts (to select your disk, etc)
Click the Install button


Once completed, your MBP will restart as normal. This process does not erase your drive and therefore all your apps and data should still be in place. In other words, this process does nothing but reinstall macOS over the previous version on your drive.

IMPORTANT: - Once again, things can go wrong and you should have a backup regime in place. Proceeding without a backup is done at your own risk.