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This is such an incredibly broad question which would take a considerable amount of time to properly answer.
For the most part, countries in Africa are extremely corrupt. Any sort of aid that is received is kept amongst the country's oligarchs.
Furthermore, the infrastructure is incredibly bad in many areas making commerce difficult, dissuading foreign investors.
There is little foreign investment because the economies of some of these countries are disturbingly difficult to do business in. The complexity of the laws make it very hard for an industry to locate itself in Africa
Even in the countries where it is not so difficult to start a business or invest in, you have the problem of security. Many countries in Africa have a weak internal security apparatuses, which is an unnecessary risk for corporations an entrepreneurs who prefer to protect their assets.
That leads me into many of the conflicts that take place in Africa as well. This is another unnecessary security risk for some.
The workforce is largely unskilled and uneducated...In most cases, like in Asia, some companies would assemble factories for these unskilled population to work in, but as we have mentioned the infrastructure is so bad that it makes it difficult for some corporations to set up shop.
Africa is largely a resource-based economy, meaning they don't produce anything and their exports are raw materials and minerals, like: Oil, lumber, steal. These resources go to countries like China who then assemble the good and maybe sell them or move them hand them over to a distributor in another country
Agriculture is the largest export for most(?) of these countries. While their goods are extremely inexpensive there are several factors which make them uncompetitive in the global market. Subsidies are a huge problem for Africa, they cannot compete with the likes of the U.S. who shell billions of money to it's farmers to keep their product competitive...If entities like the European Union didn't have such subsidies, it would be logical to assume that they would begin importing more much agriculture from Africa.
Banking. It is so ridiculously difficult for someone a business to obtain a loan. Think about it. Small businesses in the U.S. rely on those small business loans to get started or use an investment for equipment to help make their business more efficient which in turn might increase net profits. In Africa, institutions like these are not widely available. It's not like a person in Africa can take out a 2nd mortgage on their 400k house to start a business...However, there are a lot of ngo's that allow you to personally give a micro-loan ($50-$250) to small businesses in Africa, I highly encourage you to look into this.
By combining the last two points about farming and loans, it is difficult for any farmer to get ahead. The methods in which they use are so outdated and just very difficult for them to produce the same kind of food that other countries are able to do with these more technologically advanced methods. Perhaps if they were able to get a small loan they could buy the equipment needed to become more efficient farmers.
Also, and someone can chime in here because I am not entirely certain, but the shorelines are not favorable for cargo ships. There are minimal natural ports for cargo ships which play a role in the development of trade
That's about all I can think of off the top of my head. I know someone smarter than me can help me fill in the missing key points, but I think this should give you a general idea.
This is a widely researched topic, I encourage you to google it, as you will find an endless amount of information.