It's a massive topic, with hundreds (thousands?) of databases. The only "simple" instruction would be to put a name into the general search engine and then look at the explosion of results one by one. But, of course, that is what they want to avoid. They want a "simple" way to get the exact answer they need. And if they knew what that answer was, they wouldn't be asking us.
The trick is knowing how to ask questions in a way that will give you only a few answers. To do that, you need to become familiar with the databases' categories, and the rules Ancestry uses to search them. Often, the best way to search is to pick out a specific database or subset that focuses on what you want. Military records? Consider focusing on the enlistment subset. Passenger list? See what is available for the time the ancestor arrived. Census search? Pick a specific year. Don't forget city directories between census years. Learn the limits of each database: What is missing?
The easiest way to learn the ins and outs of any database in PWPL's Digital Library is to click on the vertical tab to the left, "Digital Library Tutorials." That tab will take you to Niche Academy, providing short tutorials about many databases offered through the Digital Library.
For Ancestry.com: Library Edition, that link looks similar to Ancestry's home page. The tutorial will give you plenty of tips about getting started and understanding many of the records Ancestry.com: Library Edition provides. HeritageQuest Online, an offshoot of Ancestry, has a tab called "Research Aids" that also helps you get started and includes historical maps of each state in the Union.
Remember, if you have a specific question about one of our online databases, feel free to contact us to see if we can untangle it for you. Call 703-792-8380 or email relic2@pwcgov.org.