Fallout 4 is all about the player being entrenched in its rich Boston Wasteland. Part of this means crafting and repairing all of your tools for survival, including your Power Armor.
These huge suits can protect you from quite a bit of damage, but they cannot do so indefinitely. After enough bullets, laser blasts, explosions, and vicious melee attacks, some pieces will lose their armor entirely. Luckily, you can easily repair anything that’s damaged.
Park your Power Armor in a Power Armor Station then exit it and interact with the station through the Craft command. Now, highlight the part of your Power Armor that needs repairing and press the Repair button. When you do this, a prompt telling you how much material will be used (Steel) and whether or not you want to proceed will pop up.
Choose yes and there you go. Just do this to all parts that need the attention and your Power Armor in Fallout 4 is as good as new.