This is an example.
You create a profile, with a context and a task (action or list of actions). The actions take place when teh context criteria is met.
First you need to set a new profile all. Perhaps called "Scheduled SMS".
So New>"Scheduled SMS"
Then add a context. Add Day (you can shoose a date under month day or a week day under week day).
Then add a task (Named "Send sms" for example). Click the + button in the task and select "phone". Select "Compose sms".
Add the number.
Add the message.
Click Done and Done again. At the profile list, click on the weekday / month date context you added and select "add". Now if you wish, you can set a time (i would otherwise it would happen at midnight)..