How do I add Git version control (Bitbucket) to an existing source code folder?

Final working solution
using @Arrigo response and @Samitha Chathuranga comment, I’ll put all together to build a full response for this question:

1. Suppose you have your project folder on PC;

2. Create a new repository on bitbucket:
   

3. Press on I have an existing project:
   

4. Open Git CMD console and type command 1 from second picture(go to your project folder on your PC)

5. Type command git init

6. Type command git add --all

7. Type command 2 from second picture (git remote add origin YOUR_LINK_TO_REPO)

8. Type command git commit -m "my first commit"

9. Type command git push -u origin master

Note: if you get error unable to detect email or name, just type following commands after 5th step:

 git config --global user.email "yourEmail"  #your email at Bitbucket
 git config --global user.name "yourName"  #your name at Bitbucket