We know that the waters of Mormon were quite some distance from the city of Lehi-Nephi because sometime later an apostate group built a large city there called Jerusalem. This city is referred to in Alma 21:1-2 as being built on the borders of Mormon.
It appears that about this time Alma began to enjoy the ministering of angels. We know this from the fact that in verse 18 we read that he had received the holy priesthood. Alma 5:3 says he had been ordained a high priest to preside over the Church, and he used this authority from God to ordain other priests. We also learn that he knew how to initiate the ordinance of baptism. This included the procedure by which he would be baptized himself when there was no one with authority to do it for him. According to verse 17 he was taught how to set up the church of God, or church of Christ, and all of these things came to him by direct revelation while he was in the thicket near the waters of Mormon.