How do I make a booster library?

[Rename_22]

I am a relatively new ksp 1 player and I am trying to build a new eve station (it’s my first time doing this) I have split it into 4 segments and don’t want to spend time and just reuse the same booster for each part of the ship instead of building a new one each time I have heard streamers mention “a booster library” I think this might be a way to reuse boosters but I could not find anything on the internet to help me. Please can someone explain to me how to make one? I can’t find a way to save boosters in the VAB nor a way to open two saves at once 

[Bej Kerman]

1 hour ago, Rename_22 said:

I am a relatively new ksp 1 player and I am trying to build a new eve station (it’s my first time doing this) I have split it into 4 segments and don’t want to spend time and just reuse the same booster for each part of the ship instead of building a new one each time I have heard streamers mention “a booster library” I think this might be a way to reuse boosters but I could not find anything on the internet to help me. Please can someone explain to me how to make one? I can’t find a way to save boosters in the VAB nor a way to open two saves at once 

It sounds like they're talking about subassemblies (accessible from the advanced parts menu). You can drag and drop a group of parts into the subassembly list and retrieve it later. Make sure the part of the booster you're attaching payloads to is the root.