The team at LiquidEOS by Bancor have made a very super-easy user-friendly standalone desktop application which allows you to vote for your Block Producer candidates.
Even though it's already very easy, I have decided to make a picture tutorial to help those who are struggling and to demonstrate just how easy it is.
Step 1: Go to the website and download the voting tool at http://vote.liquideos.com/ Make sure to choose correctly. If you have an Apple computer it will be For Mac, all else would be Windows.
Step 2:
Click Next
Step 3:
Enter your private key
Optional: You can verify and/or copy your account name down. This will be useful later on.
Step 4:
Finished
That wasn't so hard was it? :)
To verify the votes on the blockchain, you can use the explorer at https://eosflare.io/ and paste in your Account Name [Not your private key!] to verify your votes went through.