There is a comprehensive range of online design courses to choose between, but it all depends on what you want to get out of the course. Some of these will be more focused on graphic design and print design, while others will be focussed on websites.
If you’re not entirely sure on the area of design you’d like to get into, then it’s important to start researching to get a better idea. There’s no doubt about it, design skills are transferrable so you can switch between different jobs quite easily, yet website design is going to require knowledge of HTML and CSS, so there are some technical aspects to get your head round.
Many different websites offer online design courses and you should always look at the reviews before you come to a decision. Most will provide interactive interfaces, and the possibility to learn as you go, whilst repeating stages if and when you feel you need to.