Viewing your website users web browser, operating system and screen resolution is handy for several reasons.
For user experience, Internet explorer for example is well documented to be incompatible with modern web technologies, seeing most of your website visitors using internet explorer is going to make you design your website differently. Knowing popular resolution is excellent in shaping how your responsive website looks at different ratios.
Here is how to view your website visitors browser, operating system and display resolution in Google Analytics;
Go to the Google analytics dashboard for the website you want the viewers browser details for. On the left hand panel find audience and click it, now click Technology and then finally Browser & OS. See the image below
This will display your websites users web browsers they used to view and navigate your website with. That days range for this data is dependent on what you have set. Check the top right to see the date range.