You can check how many credits you have left by selecting the profile drop down on the top right hand side.
When sending emails, it costs one email credit to send one email, and it costs one sms credit to send one sms (unless you select multipart messages, in which case it may be more depending on the length of the SMS message).
If you would like more credits, contact your Account Manager or email accountmanagers@pure360.com.
They will also be able to tell you the different rates for credits, how many you last purchased and how many credits you are currently using.