How to mix a resurfacer/leveler with sand and cement?
Roughen all areas to be resurfaced, remove any loose or unstable material. Dry mix 5 parts fine sand to 1 part portland cement. Moisten entire area to be resurfaced. Add small amounts of water, a little bit at a time, and thoroughly mix until entire batch is damp. For initial dry-pack, proper mix should hold as a clump if you squeeze together in your hand, but easily come apart if you break it up. For your resurfacing purpose, it could be a bit wetter but not liquidy. Spread out and pack firmly into area in question with a wood float, use the wood float to feather the edges of the repair into existing surface. Use a spray bottle to moisten as needed while you float it out. Screed or float out as level as you need it to be but the surface does not have to be super smooth.

Apply water-proofing membrane, then apply additional treatments (float regular cement on top of membrane then install tile?). Drypack is most often used to establish initial slope for the surface, not for applying final finish treatment to.