Get the concrete floor completely clean with floor cleaner and a mop. Let dry at least 24 hours.
Lay the 2x4 on its narrow edge along one side of the floor. Scoot the board slowly forward over the floor, watching the surface of the floor where it meets the board. Anywhere there is a space between the board and the floor (indicating a low spot in the floor) circle the area with your pencil.
Mix floor leveler and water in your bucket, in the amounts called for on the leveler packaging. Use your drill and mixing bit to mix it. The mixed leveler should be almost as thin as water.
Pour the leveler slowly over each of the areas that you circled, letting it spread out and fill the low spots. If any of the leveler doesn't completely level itself out, scrape your 2x4 over the area to flatten it. Work your way across the whole floor.
Let the leveler set for 12 hours. The floor is now ready for linoleum tiles.