Hey Eric_S,
Glad to hear you're starting the SEO 101 journey.
1. You can view which keywords your site currently ranks for on a domain level or a page level through using the MOZ keyword explorer tool, selecting either "domain" or "page" and inputting the URL into the tool. It should then show you a list of all of the keywords and their volumes. This can also be done using tools like SEMrush or AHREFS.
In order to view the search traffic on your site, you will have to look at its Google Analytics data, or any other tracking program you may be utilizing and sort the data to find out the number of users that come to your site via organic search. (This is a little vague, and will vary depending on which program you're using for analytics, so feel free to ask for clarification or do further program-specific research.)
2. Excel or google sheets both work well for keyword documents.
3. There are a lot of different analysis that can be made by finding the keywords you currently rank for. You can find keywords with higher volumes that you would like to rank higher for, and try to re target pages to achieve this.
Simply having a keyword mapping document outlining the targeted keyword for each page can also be useful when writing things such as titles and h1s on a page. It really depends on your goal.
I hope this was helpful!
Lydia