The Web Terminal's sub feature makes it much easier for people to find substitutes when they can't serve at their scheduled times, and we highly recommended that you take advantage of this feature.
NOTE: On the Web Terminal, the text is "Request a sub", however within MSP, the term "Swap" is used to mean "Sub" (this is because within MSP "sub" is already defined as a substitute volunteer)
The way it works is that a volunteer logs into the Web Terminal and goes to their My Schedule tab to see a list of their upcoming services. If they can't make one of their scheduled times, they click the "(request sub)" hyperlink next to that service.
What happens next depends on the set up of your Web Terminal. If you do not have swap requests set up to be processed automatically, then you will receive a "Swap request" web form that you will need to process by going to the Web Forms pane inside MSP.
If swap request forms are setup to be automatically processed, then the form is processed automatically and immediately. Whenever the form is processed, the position will then be flagged as "Swap requested" in your schedule, and it will appear in the "swap requested position list" in the "My Schedule" tab of the Web Terminal for all ministers that are qualified to fill the position.
Additionally, depending on your Web Terminal settings, an email may be sent to all volunteers that are qualified to fill the position notifying them that the swap request was made.
If you do have the Web Terminal setup so that volunteers are sent the notification email (recommended), then the volunteers that receive the email can click on a link right there in the email to volunteer to fill the position. If not, then when a volunteer who is qualified to fill the position logs into their Web Terminal to check their schedule, on their My Schedule tab they will see the "swap requested position list" which contains all the positions that are up for grabs. Each position will have a "(volunteer now)" link next to it, and by clicking the link next to a given position they can volunteer to fill that position.
If you have chosen to allow volunteers to propose trades, see the OKB article on how this feature works to learn more. Once a volunteer has signed up to fill the position, what happens next again depends on your Web Terminal settings. If automatic processing is not turned on for swap accept forms, you will receive a "Swap accept" web form that you will need to process by going to the Web Forms pane inside MSP. If swap accept forms are setup to be automatically processed, then the form is processed automatically and immediately. Whenever the form is processed, the swap is made and the schedule is updated inside MSP and in any full schedules posted in the Web Terminal. A confirmation email is optionally sent to both the volunteer who requested the swap and the volunteer who accepted. (If two volunteers should volunteer to fill the position while it is still up for grabs, which can only happen if automatic processing is turned OFF, the volunteer who submitted the form that is processed first will be given the position, and this volunteer will receive the confirmation email. The other volunteer will not receive a confirmation email, and can therefore assume that they were not needed.)
If you go to the Home tab of the Web Terminal pane inside MSP and click the "Web Terminal settings..." button, you can access the settings that control which forms should be processed automatically and which should be processed manually, and you can set up emails to go out when swaps are requested and / or accepted. You can also alter the text in the emails by clicking on the "Edit Email Body..." button to reflect whatever instructions you feel would be best for your volunteers.
Regardless of whether manual or automatic processing is used, you can always see a record of which volunteers swapped on which dates by going into the Web Forms pane inside MSP and clicking on the "Processed forms" option at the top of the pane. Moreover, you can use MSP's attendance reports to see a breakdown of how many times each volunteer has requested or accepted swaps. These reports can be accessed through the "Reports" menu at the top of any open schedule window.