Basic Armor Rules
You can’t benefit from the use of armor unless you are considered proficient in it. This can be done through picking the armor type in character creation, training, or getting on of the abilities that gives you proficiency in an entire type of armor in.
Wearing armor without being proficient doesn’t change your armor class and gives all other creatures advantage on attacking you
Anyone can use a shield, you don’t need proficiency with it
Taking Armor On & Off
Taking armor on and off takes a full turn. This means you can’t use your action, bonus action, reaction, extra actions, free actions, or movement. However, the armor will be considered on you at the start of your next turn.
Shields can be easily taken on and off as an extra action.