Both are plugins for eclipse that make it easier to work with Spring. Spring IDE has a more limited set of tools, whereas STS is a more professional toolkit.
Both can be installed from the Eclipse Marketplace.
Here are the instructions to install STS in Kepler:
1) Go to Help->Eclipse Marketplace...
2) Search for "Spring".
3) Select "Spring Tool Suite (STS) for Eclipse Kepler" and click install
4) Restart Eclipse
At this point you should be able to create a project:
1) Select File->New->Other
2) Type in "Spring" and select "Spring project"
3) Follow the procedure to the end. You can also select the type of the project under "Templates".
In alternative you can download a version of STS already integrated with Eclipse from here:
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