Installation and configuration
Mforms is a library, so by itself it does not provide any functionality (besides the real-life examples in the mforms example module). Therefore there is no configuration or installation besides enabling the module in the module list.
Included module mforms_example contains several real life examples that are documented in code. To find out what it does visit /mforms page after you enable mforms_example module.
For faster dive into mforms here is the basic architecture:
STORE_KEY - not just identifies the storage slot for submitted values, it represents the identifier of whole multi-step form implementation.
Steps file - The file where individual form steps with their validate and submit callbacks reside. See mforms_example/mforms/mforms_example.session_store_example.inc for demonstration. This file must be named in the following pattern: MODULE_NAME.STORE_KEY.inc and placed in "mforms" directory of the module in which you are implementing the multi step form.
Store object - MformsIstore implementation responsible for storing submitted values and internal mforms data needed to control the stepping process.
Steps object - it is aware of all steps, current step, next step and previous step.
Controls object - the UI control object. It controls the form buttons.
Initialization process consists of instantiation of store, steps and controls objects and calling mforms_init_module() function into which you pass these instantiated objects. You can do this in a Drupal page callback followed by call of drupal_get_form(). However this approach will not allow you to handle ajax calls.
The proper way is to implement hook_STORE_KEY_mforms_init() and
within this hook implementation do all initialization - see mforms_example.module, function mforms_example_fs_store_example_mforms_init().
Drupal form callbacks
The form lifecycle is handeled by Drupal. Therefore there must be regular form callbacks: FORM_ID(), FORM_ID_validate() and FORM_ID_sbumit(). Inside these mforms takes over as can be seen in the mforms_example.pages.inc, i.e. functions mforms_example_fs_form[validate, submit]().