For a short overview of the Revolution packages, you could have a look here:
http://marcoraven.net/modx/revolutionpackages.html
TinyMCE and CKEditor are two possible rich text editors for the MODx manager (mentioned under the header of "Some popular backend only modules").
If I understand it correctly CKEditor is now the advised solution, because it is more stable than TinyMCE, but I must admit that I still use TinyMCE.
Uploading images can be started from the rich text editor (click on the small picture to get an overview of the pictures already there, and on the icon there to add files) - but will in fact be done with the file manager (at least it looks that way to me).
The file manager can be accessed directly: look at the tabs at the left of the Manager UI - there are tabs for Resources, Elements and Files - the last one is the one you want. Click on the directory where you want to add you file; choose add, select your file and choose upload.