What is the flex position? What am I looking for to put in that spot? WR2 RB2?
Most leagues will start 1QB, 2 RBs, 2 WRs, 1 TE, and 1 flex. Most commonly the flex can be used for a RB, WR, or TE. Check with the commissioner or the settings of your league to find out for sure. It could be a super flex which allows for a 2nd QB and that changes everything.
The flex position is just that, a position where you can use players from different positions. As for who to play there, it completely depends on your team makeup. I tend to use RBs or WRs with good matchups or potential for a boom week. A hot WW pickup can fill in very well.
Last year, I had Tyreek Hill fill the flex in one of my leagues. It was very nice not to have rely on him for a weekly base but to get the absolute boom (his return yards and TDs counted)! He helped me to the