The processional is the moment you and your wedding party enter into the ceremony space and get into place for everything to start. The traditional processional is becoming less and less common as couples embrace doing things a bit different then they used to. There is a lot of optionality within the processional and it's a chance to personalize how you'd like your ceremony to take place.
At the start of the ceremony I like to go up and make an initial welcome announcement to your guests and get them ready and engaged before the formal processional takes off.
Traditionally the processional starts with the grandparents entering. As couples get married later in life it is very common that the grandparents will be seated already and opt not to be a part of the processional. This leads to myself, or whomever your officiant is, being the first to enter. Some couples choose to have the Groom and groomsmen enter with the Officiant casually and stand up front before the formal processional begins. Others choose to send only the groomsmen with the officiant. If that's the case the Groom may enter formally with both of his parents and seat them. I like to remind Grooms to give their parents a hug and a kiss in this moment. Others opt to have the Groom be the start of the formal processional followed by his groomsmen. If the Bride is walking with only her father, some choose to have the Groom or the Best Man walk the Mother of the Bride down the aisle and seat her.
After the groomsmen, the bridesmaids will enter. The Maid of Honor will be the final member of the wedding party to enter. Following the Maid of Honor will be the ever important ring bearer followed by the flower girl who will lay a bed of flower pedals for the bride to enter on.
As the Bride prepares to enter the guests may be asked to stand, as is customary. Traditionally the Bride is walked down the aisle by her father. Many brides are now choosing to be walked down the aisle by both of her parents. When the Bride and her father or parents reach the front I recommend they hug and kiss both the Bride and the Groom. This is a nice moment and sets the tone for the entire ceremony and makes for a good photo opportunity. As the Bride takes her place up front with the Groom, Officiant and the rest of the wedding party the ceremony is ready to begin.