Can I name a guardian using your service?

Yes, this is a very important part of our service.
As you step through our service, you will be asked to identify if you have any children, and enter their dates of birth.

If your children are minors according to the laws of your State, you will be prompted later to name guardians for those children

Your guardian selection will then appear in your Will.
It is important to understand the process though.
In reality what happens is that if neither parent is available, then a judge at the family courts will appoint a guardian. Hopefully people will come forward and offer themselves as the guardian and the judge will grant guardianship to the person or family that he/she considers to be the most appropriate. As a parent, the stated appointment in your Will would be the over-riding factor in making that appointment, together with any appointment made in the child's other parent's Will. If this person is still willing and able to serve as the guardian, then the judge would most likely grant guardianship to this person.
Of course, circumstances can change between the writing of the Will and the guardianship appointment being made. For example, your guardian may have personal struggles of their own and are no longer fit to look after your children. This is why your guardianship appointment in your Will is not a legally binding appointment.
But unless there is some reason why the person that you have appointed in your Will is unwilling or unable to act, then they will almost certainly be appointed the guardian to your children.