I would like this opportunity to give a shout-out to Udemy, a website where they offer an extreme amount of online courses in many different subjects. By now I have purchased about 6 courses from the website, which all gave me new tools to use building my websites and even taught me how to build my own games and applications.
The first course I have completed is about WordPress development. WordPress is the most used Content Management System (CMS). It's very customizable and very intuitive, making it the ideal CMS to build my websites in. It gives the end-user the chance to keep his or her own website updated without any coding knowledge.
The second course I'm planning to finish in the near future includes a section that introduced me to Bootstrap 4. Bootstrap is a library that makes building smooth responsive websites a lot easier. At this point of time, I build all my new websites based on Bootstrap 4. By combining Bootstrap 4 with the WordPress CMS, you website will look stunning on every device and is really easy to maintain!
Of course, I keep developing my skills with the help of more and more courses. Why not have a look if they have a course that offers learning something you've always wanted to learn? They have plenty of categories available besides the development courses I have been following.

One advice: always look a couple of preview videos of the course you are interested in. To me it's important that I'm OK with the voice of the instructor, as I'll be spending a lot of time listening to it. Check out of the instructor suits you, before purchasing your course.