Leveled spells are used by NPCs and are much like leveled items. NPCs with leveled spells don't actually have any spells in their spell lists until the Player enters the same cell as them. Once these NPCs get loaded, the spells they get are chosen from the leveled spell list based on the Player's level.
For example, say a Bandit Hedge Wizard has LL0FireDamTargetMinor100 in his spell list.
In that list, the spell called Flare will definitely be added when the Player is at levels 1-24, while Flash Bolt
might be added at level 25+. Flare might still be selected because 'Calculate from all levels < = PC's level' is checked. It's also pissible for both spells to be added at levels 25+ because 'Calculate for each item in count' is checked.
If you're wanting a spell that will level up with the Player even if you start with it, there aren't any in vanilla. I'm pretty sure there are mods with spells like that, but I don't know them.