Filtration! Filtration! Filtration!
For a successful planted aquarium it is a de facto requirement to have some kind of external filtering (canister, typically) with a (nominal) capacity to process 10 times the tank volume in every hour. Having high quality biological filter media is also a basic requirement — many aquascapers replace sponges and mechanical filters with high-grade (that is not the plastic balls sometimes delivered with the filters) biological media in their canisters. Finally, there are some high-grade chemical water purifiers that removes all the excess colour and odour that may be left in the water, such as Seachem’s Purigen.
But having clean water will not resolve algae issues automatically, this is a whole new story with quite a bit of complexity :) The algae that grows on the side of the tank (assuming it is green) may be related to exposure to direct sunlight / too much light and/or low phosphate levels, read more here, for example.
I wish you best of luck with the hobby!