Making Port O'nor
First, to cast a spell you must have access to it, either from your class, a magic item, or some other source. Certain classes also require that you have the spell prepared in advance.
Second, in combat, you must cast a spell as an Action, unless a spell’s descriptions says otherwise. Outside combat, you can effectively cast a spell whenever you want, but you must complete one spell before casting the next.
A spell’s components are the physical requirements you must meet in order to cast it. Unless a spell’s description says otherwise, a spell requires you to chant mystic words, which constitutes its verbal component, and to have use of at least one arm to gesture, which constitutes the spell’s somatic component. Some spells also have material components, particular items, or objects that are required for the casting.
If you can’t provide a spell’s components, you are unable to cast the spell. Thus, if you are silenced or your arms are bound, you cannot cast a spell.
Casting in Armor
Because of the mental focus and precise gestures required for spellcasting, you must be proficient with the armor you are wearing to cast a spell. You are otherwise too distracted and physically hampered by your armor for spellcasting.
Casting a Spell at a Higher Level
When you cast a spell using a spell slot that is of a higher level than the spell, the spell assumes the higher level for that casting. For instance, if you cast the 3rd-level spell fireball using a 5th level slot, that fireball is 5th level.
Some spells have more powerful effects when cast at a higher level, as detailed in the spell’s description called At Higher Levels.
Casting a spell requires an amount of time specified int he spell. Most spells require a single action to cast, a few seconds of time during which you recite a magical word or phrase and complete a set of hand motions.
Longer Casting Times