Encyclopedias are collections of articles - some a paragraph long, some several pages long - that give a broad overview of a particular topic. Each encyclopedia has a different theme, and each article will sort of "speak" to that theme. For example, an encyclopedia on the history of food in Europe will have several more specific articles covering topics specific to food and eating (food customs, types of food, methods of cooking). These are great for gathering: timelines, information on important events and people, and additional keywords. You can then use these as a jumping off point to search for more "scholarly" sources. It's like Wikipedia - but better!
Remember: These are not "scholarly" - they do not incorporate original research studies, but rather provide a more "factual" overview of a topic. these are jumping off points for scholarly sources. (Example: You could find what major events were occurring and match these up to the approximate years your ancestors migrated.)
Oxford, Sage, and Gale each offer a suite of online reference materials. Search these for preliminary information on cultural history, social, political and economic history for your country or topic.
These will search across NUMEROUS encyclopedias. So this is a good place to start, to capture a number of articles - and keywords - on your chosen region or country.
Reference books contain the actual articles you will read to get a sense of what was happening in the country or region under study during the time your ancestors lived there or migrated. If you know what you want to focus on (food, economy, occupations), you can hone in on that specific encyclopedia. Below are a few examples.