The first thing you should do go to each page's social media settings Page>Settings>Social Media and enter a default tweet that will populate Twitter when someone clicks to share via Twitter. Even more importantly, below that is the Facebook and SEO excerpt which should give a brief description of the most important thing about that page.
There is really nothing to edit on the home page as it is made up of partial templates contained in the home_hero.html and homepage_layout.html files. If you change the site's header image, it will change the home hero image and the banner image on any subpages that don't have their own specific banner image.
The Navigation bar at the top of the homepage is actually the nav.html file so if you add or delete any items from the Top Nav those changes will be reflected in the top hero nav and well as the nav bars on all the subpages.
My Priorities is a blog page. The introduction is the first post and the subsequent 6 issues are blog posts. The images on the homepage are simply image files uploaded to each priority post. If you want to change the image, just delete the current image and upload a new one. The red text on the homepage are the headlines of each issue blog post. If you want to change the text of any of the posts, go to My Priorities>Posts and Subpages and you will see the recent posts. Click on one and edit the text.
The text of the Meet Michael page is the content of the About Page. The text on the homepage in the Meet Michael section is from the content of the subpage About Text. If you want to change the header image of the Meet Michael page, go to the files section, delete the current image with the word banner in it and upload a new image with the word banner. If you want to change the image of the section on the homepage, delete the image with the word grid in it and upload a new one.
Go to Page>Volunteer Settings. If you scroll down you will see the content editor where you can change the text. Towards the top of the page on the left-hand side, you will see Roles and Auto Response. Click on Roles to edit, add or delete roles. You can also drag and drop to change the order in which the roles appear. For each activity, I recommend add a specific tag to that role so that you can search for volunteers in the people section by activity type. For example, if you arrange for a day of door knocking, you could filter for people who have the tag "doors" and send a blast email to only those people. You will get a better response rate if you are specific with your ask.
Even though it is not publicly visible, there is a Calendar page. You can set up a volunteer activity as an event and send the link in your email allowing people to RSVP online.