Turn off show tier number in the game's settings to stop the tier from showing in your current selection. There are other choices in Aslain's installer if you really do want to see what tier the tanks are. I use Modern with Arab Tiers.
What you circled (from left to right): Average tier of tank the player owns, number of matches in current tank, win percentage in current tank and I believe ratio of average done in tank vs. tank's hitpoints.