All cast iron surfaces need to be covered with a protective coating. Otherwise they develop rust when exposed to air and water.
Simply applying any product to your machine's top won't do. The product cannot be tacky. That would keep the stock from sliding.
Some products have a negative effect on any wood they come in contact with. Oils, for example, will soak into the pores of wood and prevent any finish from taking hold. The result is spots all over your work.
Apply a coat of wax
Woodworkers seem to agree that
Johnson's paste wax(on Amazon) works best. It protects the metal, creates a slick surface for the work pieces to glide on, and does not impact the wood in any way.You can find Johnson's paste wax in almost all home centers at a fairly inexpensive price. No need to go high-tech and high-price.
Apply a liberal amount to to the surface. Work the wax into the surface with a rag for a while. If the surface is cold, it will take longer for the was to bond properly. Rubbing heats up the wax and helps it flow better. A heat gun or a hair drier can help getting to an even finish faster.
Once the entire surface is covered, wipe off the excess. Most of the wax you have just applied will come off again. That's ok. The desired outcome is a layer of wax so thin you cannot see it. As long as you only use medium pressure, the layer left behind will be thick enough.
Durability of the wax coat
Once you are done, you top is protected. If you do not use the saw, the wax will stay in place indefinitely. Usage does wear through the layer ever so slowly.
A commercial shop should reapply the wax every month. In a residential shop, once a year is often enough.
SlipIt Woodworker's Sliding Compound (on Amazon) performs with mixed result. It does prevent rust, but requires more frequent applications. It's thinner consistency makes it harder to apply without making a mess. It's higher price and low availability make it a clear second choice to me.
Car wax or other products based on silicon should be avoided. They do protect the table saw, but they will also leave deposits on your wood that will interfere with some finishes.
Johnson's past wax is the tried and true method for caring for your cast iron woodworking machines. Apply it once or twice a year and your machines are protected.