can your employer make you pray before you start your shift at work

Typically most employment is "at wll", which means that an employer can generally set the conditions of the workplace much as it sees fit. However there are some exceptions to this. First of all, an employer's actions must not violate the terms of any applicable union agreement or employment contract. Secodly, an employee's treatment cannot constitute some form of legally actionable discrimination, and harrassment is included. In this instance, you appear to have a claim based on your employers mandating a prayer before work. Such religious harassment is in violation of federal law. Specifically, it occurs when an employee is “required or coerced to abandon, alter, or adopt a religious practice as a condition of employment". That having been said, there are certain requirements that must be met  in order to prevail in a such a lawsuit. Additionally, all employers (private and state/local governments) are covered under the law but with some exceptions, such as religious organizations and some employers with fewer than 15 employees.
To be certain of your rights, you should contact your state's department of labor and/or consult directly with an employment law attorney in your area.

No, an employer may NOT do this: requiring prayer is violation of employment discrimination law, which means (among other things) that an employer may not require religious activity from its employees. You could file a complaint about this with the federal EEOC or your state's equal/civil rights agency.