The methods by which you and other users can join meet me conferences depends on your system administrator. They may configure special numbers that you can dial for each particular conference or to be prompted to enter the conference number.
However, if your system supports the Call/Conference Scheduling gadget, you can use its meetings view to join any meet me conference you scheduled or to which you have been invited.
To do this, in the Meetings View, locate the meeting and click the 
icon.