It's simple! There are several ways to accept an assignment - and it depends on how the MSP published it. Most assignments are available to self-assign (you can grab it if you want it) and others must be requested (a scheduler decides who gets it).
Whether you are using the website or an iSecretShop smartphone app, click Available Shops. This will display all the currently-available shops near you (if you want to search for shops somewhere else, see: How do I find shops in another area?). Locate the shop you want and click Request.
You will be asked to enter the date you intend to perform the shop and, if it is in range, the shop is yours. The questionnaire, instructions and any attachments will be emailed to you immediately.
The same as above, but once you enter the date, your request goes into a queue and the scheduler(s) responsible for that client will award it to the shopper who best meets their criteria. If you are selected, you will get an email (as above). If you are not selected, you will receive a Decline email. Please note: there are a wide variety of reasons why a scheduler may not choose your request - that do not reflet poorly on you as a shopper. Please keep trying because next time, you may be exactly what they are looking for.