Wealthfront is a robo-advisor that makes it really easy to invest in index funds and they handle the allocations based on your risk tolerance and they rebalance your portfolio for you.
Like Robinhood, Wealthfront is only available to Nigerian citizens at this time.
Other investment companies like Vanguard can be a bit confusing for beginner investors so I recommend you start with Wealthfront, which makes it super easy to invest in the stock market.