For if I pray in another language, my spirit prays, but my understanding is unfruitful. What is it then? I will pray with the spirit, and I will pray with the understanding also. I will sing with the spirit, and I will sing with the understanding also. I thank my God, I speak with other languages more than you all. (1 Corinthians 14:14, 15, 18)
What is prayer in in the Spirit? It is praying in a language that you have never consciously learned, by the inspiration of the HolySpirit (Acts 2:4).
It happens through your spirit (1 Corinthians 14:14-15), therefore your mind is not involved, leaving you to do other things at the same time as praying in the Spirit.
The Greek word used for "language" is γλωσσαις, which quite simply is translated "tongue," and by implication "language." The word for "other" is ετεραις and is where we get our English word "hetero" meaning a different kind. The languages that the HolySpirit inspires God's people to pray, worship and speak in, are not "made-up" or gibberish. There are over 6000 known human languages on planet earth, and an unknown amount of heavenly, spiritual languages, so it is impossible to judge them in the flesh.
It is not done with, or a creation of, the mind. Those who have not been born again by faith in the Lord Jesus, and subsequently baptized into His Spirit, simply do not have this ability. It is the Spirit Who speaks through the believer, as they cooperate with Him (Romans 8:26).
Those so baptized in the Spirit must cooperate, in the same way that those who prophesied (and those who still do today) had to consciously speak out the prophecies that they received from God (1 Corinthians 14:32). The Spirit will not move your mouth; He will only give you the inspiration in your spirit. As seen above in (Romans 8:26) it is a partnership between the Spirit and the believer. He helps us with our weaknesses through His groanings that can't be uttered. These unutterable groanings are given a voice when we come together with Him (1 Corinthians 14:15).
This section will look at the many ways that praying with the Spirit's help in other languages given by Him will accomplish the will of Yahweh.
26In the same way, the Spirit also helps our weaknesses, for we don't know how to pray as we ought. But the Spirit himself makes intercession for us with groanings which can't be uttered. 27He who searches the hearts knows what is on the Spirit's mind, because he makes intercession for the saints according to God. 28We know that all things work together for good for those who love God, to those who are called according to his purpose. (Romans 8:26-28)