I read that but i don't understand what it says about the R8 maybe someone can put it in simpler terms
R8
This is the "source resistor" for the op-amp's class A biasing cascode. See this section for details of how this works.
To go through the value picking procedure described in that section, you will probably need a good selection of values in the 10Ω to 1KΩ range. You can use cheap 5% carbon resistors here, and just get a few of each of the E24 values in that range. (10, 11, 12, 13, 15, 16, 18, 20 ohms...) If you really wanted to be frugal, you could limit the range to the 47Ω to 470Ω range. You may also consider getting a 5% resistor selection kit, which many manufacturers offer.
Optional? Yes. You can jumper it in some situations if you're using the cascodes, and if you're not using the cascodes you should leave it empty.