When you "put work into" something, it means that you work hard on it. You use the phrase "put work into ___" when you're talking about projects that need a lot of work, and take a while to finish. For example, you might "put a lot of work into":

• a big presentation for work
• an essay for school
• a website that you built

The adjective phrase "a lot of" is commonly used with "put work into ___". For example:

The Patzers bought their house for $ 125,000 in the early 1990s and put a lot of work into it, including some indoor remodeling.