Analyzing TRMM daily precipitation data by season and spatial plotting

Hello. I downloaded 20 years worth (1998-2018) of TRMM (.nc4 files) daily precipitation data. I have to analyze this data by season; summer (June-July-August), fall (September-October-November), winter (December-January-February), and spring (March-April-May).

I then have to plot this data spatially for the contigous United States. How do I go about it? I am brand new to this. Your help is greatly appreciated.