https://pokemongo.gamepress.gg/pokemon-stats-advanced
https://pokemongo.gamepress.gg/pokemon-stat-change
Basically, IVs are values from 0 to 15 that are added to the pokemon's base stats, the combined stats are then adjusted to its level and used to calculate the CP. The arc is a direct representation of the pokemon's level.
You can use this or another site's IV calculator to determine the exact IVs on both. There's also CalcyIV for Android and PokeGenie for iOS that do most of the work for you without having to input everything manually to a calculator. Calcy is an overlay that records the values from your screen while PokeGenie reads them from a screenshot you take of the pokemon.
The ingame appraisal tells you the overall IV range, then the highest IV, then the range for the highest IV. The best appraisals mean that the mon has 82% or better IVs and that the stat in question is a full 15.
