All Macs come with TextEdit which is a pretty good text processor. You can find it by clicking Spotlight (keyboard shortcut is Command - Spacebar) and type TextEdit.
However if you need a fully bodied word processor such as MS Word, there are many alternatives available. Anything from free on-line applications to Apple's Pages app (about $20) to MS Office for Mac which includes Word, Excel & Powerpoint. In short you have many many choices based on your needs.
It depens on what you mean by word processor. Included on all Macs isTextEdit which is a text editor but not a full blown editor like Microsoft Word. A free app that it a bit more capablity is BEAN. Other free apps that has more capability is OpenOffice 3.4.1.
For other possible candidatges, both free and paid, go to MacUpdate.com and search for "word processor".
OpenOffice, LibreOffice, and LyX are all excellent choices, and are available for free:
Personally I recommend LyX, but it does have a higher learning curve and is targeted mainly at technical documents. OpenOffice & LibreOffice are more similar to MS Word.