In Bucks County, most guilty plea colloquys are verbal. They are performed by the judge. In Montgomery County, they are written. You review a form and initial each page while signing the last page. In Philadelphia, the colloquy can be done by the District Attorney or the judge.
The judge will typically line up several defendants and individually address them regarding their alleged crime(s). The judge will further discuss the elements of the crimes with individual defendants and will then address the group as a whole. This will include asking if the group/individuals know what they are doing, have had time to speak to their Bucks criminal lawyer, understand they have a right to a trial, understand the burden is on the Commonwealth to prove their case beyond a reasonable doubt, and understand that they are giving up those rights by pleading guilty. The judge will also make sure you aren't on any alcohol or drugs that would preclude your ability to enter into the plea. The judge will further stress, pursuant to Padilla, that you have had time to speak to an immigration lawyer about your plea if you are not a U.S. citizen.
Therefore, the colloquy does not have to be in writing. See Commonwealth v. Yager. Remember -- you can always take back or withdrawal your plea before sentencing (which may, however, happen immediately after the colloquy). The judge will most likely go over the general elements of the crime(s) you are pleading to. The judge and/or the DA will provide a factual basis (what they are alleging) to establish a conviction. You should also review with your Bucks County criminal defense lawyer the factual basis and the potential defenses prior to entering a plea of guilty.