Spring framework is a Injection dependency framework at first (it's still as it is today) targeting managing life-cycle of Java components (what so-called beans). Today, Spring framework is pretty bloated with tons facilities/helpers on top of it; but if you look at the big picture, it's still a framework that glue things together, a middle man to MVC frameworks (Struts 1,2, JSF etc), ORM frameworks (Hibernate, iBatis, JOOQ etc) and other necessary facilities (Quartz, Email, you can tell, whatever you need, most likely, there's a Spring support). Back to our assumed flow, it takes quite a lengthy tutorial to set Spring framework up and running because Spring framework nature is to provide flexibility of choices to you.
Spring boot on the other hand is built on a totally different mantra. It's basically a suite, pre-configured, pre-sugared set of frameworks/technologies to reduce boiler plate configuration providing you the shortest way to have a Spring web application up and running with smallest line of code/configuration out-of-the-box. As you can see from there Spring Boot page, it took less than 20 LOC to have a simple RESTful application up and running with almost zero configuration. It definitely has a ton of way to configure application to match your need, this is the Spring Boot Reference Guide for your reference.
hope this answers can help you