Since you've set your About page as your front, you must go to Settings>Reading again and set "Blog" as your posts page. Then all your posts will show up when one clicks the Blog top nav tab.
Yes, you need to file your posts under various categories, depending on their content. Then you'll go to Appearance>Widgets and add the Categories widget, so that your categories will display in your sidebar. Clicking on a category will bring up all the published posts filed under that category.
Displaying the titles of all the posts in the sidebar is possible but not recommended: first, you'll have to update such a list manually each time you publish a new post; second, sooner or later that list will become inordinately long for your sidebar.
One more thing: since your theme has a top nav menu, your Pages widget is redundant. If the only reason you added it is to display the "Greeting Cards" subpage, you can go to Appearance>Menus, and create a custom top nav menu. Then the subpages can show up as dropdowns. See here for instructions:
Creating a custom menu will also allow you to eliminate the "About Hello Percy" tab (which is redundant, since you've set that page as your Home).