Though which effects are available depends on which version of the program you're using and what operating system you're working on.
The PC version of the program has Chroma Key, Bluescreen Key, Greenscreen Key and Videomerge, a simplified key effect. The Mac version has only Videomerge, which works very similarly to Chroma Key.
What version of Premiere Elements are you using and on what computer operating system is it running.
The Premiere Elements Mac users do not have Chroma Key, Blue Screen Key, or Green Screen Key. Often the Videomerge is suggested for those users as a workaround. I do not favor Videomerge.
Especially if you are a Premiere Elements Mac user (but also if you are a Premiere Elements Windows user), you might want to take a look at the Difference Matte in the keying choices.
Then you can decide what works for you.
The answers are in the details so please post more details in follow up.