For aircraft there are two main places to get both an overview and detail.
1. The database tab on the toolbar, top left of the interface. Select which category you want, such as Allied Aircraft, and each model has the relevant specs listed. The type of aircraft it is can be found in a column on the right of the table. The game chunks planes into fewer categories than in the real war to an extent, especially in the Level Bomber category, but there are enough chunks to get the job done.
2. The air unit screen repeats much of the info found in the database, but gives more data specific to that unit. There are three tabs on the bottom of the screen. Aircraft Data has details about weapons, hard-points, drop tanks, etc. , plus the various ranges in each config. There is also a Pilots tab you will be using a lot.
It is well worth studying the diagrams in the manual at the beginning, where the interface is explained. Also, just look around at things. There's no hurry to complete a turn.