These are 3 different things. Toner and essence are basically used in skin care routine while primer is a make up routine.
Toner is used just after cleansing to calm the skin, it has watery texture. It soothes skin as cleanser can be too stripping for some people.
Essence is somewhat like toner+serum and used after toner and before serum. It gives your skin the extra hydration. Exp- Snail mucin essence by Cosrx.
Primer is a silicone based thick cream which is used before foundation. You can skip it if you are not taking make up. The silicone particles in this cream/ gel makes your pores look smaller and foundation coverage is good if used after this.