Grouping columns to include only a few rows of that data

I am very new to Power BI so please bear this in mind. I have selected my columns I want to include, have loaded the data, made some visualisations using it, but I also want to include a new visual graph and use a column entitled 'employer name' which has over 1,000 rows of data of employer names, but I want to just include 5 specific companies. Do I use 'Groups' for this and, if so, how? I tried to group these five companies together and it looked like it worked, but now I am unable to get them to appear in my visualisations, and I am not sure why? Can someone explain step-by-step how I can achieve what I am looking for? (I may also want to use the same 'group' of five companies in other visualisations and if I need to do this how can I use this across all? Thanks!