You can download the Spring Tool Suite or the Spring Framework jars alone or use the maven/gradle repositories.
Using Spring Boot can make the getting started part much easier. However, a proper understanding of the non Spring Boot way of doing things will help you understand Sping Boot better.
The Spring Tool Suite is an Eclipse-powered development environment for building applications using the Spring Framework. STS comes on top of the latest Eclipse releases. STS supports application targeting to local, virtual and cloud-based servers.
It is freely available for development and internal business operations use with no time limits. There is a version of STS for most eclipse versions. You can download STS from spring.io/tools/sts/all or just do a simple Google search. The size of the download will be around 400mb.
You can go directly to the Spring Framework page @ projects.spring.io/spring-framework. Currently (as of this writing), you will see only maven/gradle based download there.
You can go to Spring projects page @ spring.io/projects for all Spring products including the Spring Framework.
You may use any IDE of your choice like Eclipse or Intellij IDEA.
Currently (as of this writing) if you go to the Spring framework official download page, you will see only maven/gradle based download. You can still download the spring jars distribution from the maven repository at http://maven.springframework.org/release/org/springframework/spring.
Note: Downloading the Spring jars directly is not a preferred approach.