Raspberry Pi 3+ Common Issues Troubleshooting Guide
In order to help you save some time, we have made this list of the most common issues when using the Raspberry Pi 3+ and how to solve them!

Boot Issues?

You finally received your Raspberry Pi and SD Card and connected everything together and see nothing more than a black or rainbow screen.
There can happen for a few different reasons but, first, you should disconnect the power and plug your SD card in your computer directly to make sure the OS has been flashed correctly. If the regular boot files are not showing, we suggest you fix your SD card issue first or try with a different one.

Unable to connect to Pi using SSH?

If you are having issues while trying to SSH into your Raspberry Pi, there are a few things you may want to review. First, make sure you have the SSH functionality in your system setting and that the IP address you are using is the correct one.

Setting up WiFi:

If you are having trouble setting up WiFi on your Raspberry Pi, you are probably using the wrong network name (SSID) or password. You can configure the WiFi using either your desktop or terminal interface.

Problems with your Keyboard characters?

If the character you see does not match the one you selected on your keyboard, you are probably using the wrong keyboard layout. You can fix this by going into your configuration tool and enter "sudo raspi-config" into the terminal. Then select "Localisation Options" and then "Change Keyboard Layout". This should match the keyboard layout to the keyboard you have connected to your Raspberry Pi.

Display Settings:

You can encounter several issues with your Raspberry display such as a wrong orientation or black bars around the edges of the screen. You can fix all these by editing a simple file in your terminal.
However, before you make any changes to your file, it is very important to keep a copy of the original. Otherwise, you will not be able to retrieve your initial settings if anything goes wrong. You can do a duplicate by using the command "sudo mv /boot/config.txt /boot/config-duplicate.txt" or simply delete the config file and rename the duplicate as config.txt.
When ready to edit the config file, use the command "sudo nano /boot/config.txt" in the terminal. Then go to the Display section of the text file and change the settings to your need. If your issue is the black edges, you'll need to alter the overscan setting and to rotate the display, just edit display_rotate.