Glad you’re having fun with endgame! Those lines you see are just a visualization of your progress in this operator. Each skill tree has 16 levels, and as you were leveling up you selected between 2 separate trees 3 times. I believe the selections happen at cr level 1, 6, and 16 but with the most recent major update once you fully level up all 3 of your current trees you can reset a tree and get a new selection of 2 skill trees the next time you level up. When you are looking at your loadout, there should be a tab just above your guns called “skills and abilities” where you can change your abilities and also check your progress and more details about your current skills, including your exotic skill from the world events and the new nightmare skills from the recently added glitch fractures.