You can easily set up drip programs that are tied to one or more trigger events (joining as a member, signing up as prospect, etc.) and then create multiple email messages to be automatically sent out with a designated timeframe (# of days past the trigger event that a message is sent). When the trigger event occurs, the series of messages are queued to be sent to the person that triggered it.
Once a program is set up, the messages are scheduled automatically. But, if you want to manually schedule a program for a given person or remove scheduled messages, simply go to the member's profile and then click on the link at the bottom for Drip Marketing Messages for this member. This shows the messages scheduled with links to remove them. There is also an add button at the top, where you can select a program, and add it to this member/prospect.