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There are sealants that you can purchase at home improvement stores. I would ask an associate for help in picking out what you will need and what prep you may need to give the walls before painting them with the sealant and what paint to use if you plan on painting the walls after sealing them.
here's how to videos for you to watch https://www.youtube.com/results?search_query=diy+sealing+basement+cinderblock+walls
It needs to be sealed from the outside. If you seal it from the inside when the water begins to seep into the basement much more water will be inside the cinder block. If it freezes it will crack the blocks.
Zard Pocleeb is right, you need to seal the outside first. That means digging around your foundation and also putting in a french drain around it to keep the water away. It will cost but better than a destroyed foundation. This is not a DIY project, get a professional, get at least 3 quotes.