So you'll concentrate on it to sustain it?<br/><br/>Ah yes concentration... you can keep one concentration spell up at a time for no actions or resources. As long as you sustain it you can't use another concentration spell (such as barkskin) without ending the first's effect. Whenever you take damage, you need to con save vs a dc of 10 or half damage (whichever is higher) to keep concentrating or become interrupted and lose the effect.<br/><br/>You can also cast spells from higher level spell slots to increase their effectiveness if the spell description gives you the option (such as sleep affecting more hp of creatures or moonbeam doing more damage)