You can turn then into content sites, set up an actual website, or try to sell that site elsewhere. You may even luck out by selling a site that's up and running and full of great content already. In this case, you can ask a higher price. Or, you can set up a shared hosting or direct hosting website. Shared hosting and direct hosting websites can be profitable too.
Hi Kulwant, these are great tips as usual. I particularly like the way to tell us to check the google pagerank in case the domain has been banned – that could lower the usefulness of the domain quite a bit. One thing though, don’t you think that buying domains is sometimes immoral? Like sometimes you accidentally buy a domain of somebody elses website who forgot to renew.
That said, my recommended budget for beginners would be $500+. Using this budget you could buy a bunch of high-potential $10 domain names, expired/dropped domain names or a mix of both. It’s very important to invest only what you can afford to lose and treat this as a side hustle till you get the momentum going. As you gain experience, industry expertise and some sales under your belt, you can then consider slowly growing your business into a full-time gig.