Some spells require you to maintain concentration in order to keep their magic active. If you lose concentration, such a spell ends
If a spell must be maintained with concentration, that fact appears in its Duration entry, and the spell specifies how long you can concentrate on it. You can end concentration at any time (no action required).
You can concentrate on multiple spells at a time, but the effort to do so increases with each additional concentration spell. Concentrating on one spell does not require any actions or movement. Concentrating on two spells costs half your movement movement speed each round, rounded down to the nearest 5 foot increment (so if your base movement speed is 25 feet, you only have 15 feet of movement available each round. Actions that grant you additional movement, such as the dash action, are not affected by this reduction). Concentrating on three spells costs your action each round. If you stop concentrating on a spell, you immediately regain the lost speed/action and can use it during your turn.
Normal activity, such as moving and attacking, doesn’t interfere with concentration. The following factors can break concentration:
Taking damage. The first time you take damage each round while you are concentrating on a spell, you must make a Constitution saving throw for each active spell to maintain your concentration on that spell (so you would need to make two separate saving throws if you are concentrating on two spells). The base DC is 8. If you succeed, record the number. If the total damage you take before the start of your next turn (including the damage from the triggering attack) exceeds this result, you lose concentration of the spell. No matter how many times you take damage in a round, you only roll one concentration check per spell.
At level 5, double the amount of damage you can take before losing concentration. At level 10, triple it. At level 15, quadruple it.