When thinking about enrolling in an online course, the first step is to decide what you want to study. That is, what kind of course you want to take? -- there are many choices available. And for an online course, the fact that you may live in Africa should not usually make much of a difference.
Once you’ve decided, then Step 2 would usually be researching online courses that are available in your chosen field. Here again, you are likely to find a wide variety of curricula, course goals, pre-requisites, formats, and costs. In Step 3, narrow your choice down to a few that seem to match up best with your own particular needs and circumstances. At that point, you may be ready to apply or enroll.
We hope these thoughts may be helpful to you. Best wishes for success as your studies continue.