Speaking in tongue comes with understanding
Normally the mind controls everything about us; the mouth only produces what the mind presented. The (unquicken) spirit therefore needs the mind.
The HS comes into us at salvation and quickens our spirit giving it the ability to commune directly to God (that is, speak in tongues).
How? It is through the same word of God- ‘open thy mouth and I will fill it’. It is about supressing your mind (which include your reasoning and language) and by faith vocalising whatever comes through your mouth.
Being by faith means the first few words may be without content but with time the spirit will take over.
Speaking in tongues is therefore giving way for the quickened spirit inside to commune with God directly (bypassing the mind).
Before there can be a quickening of your spirit so that it will be able to commune with God, you have to first receive the indwelling of the Spirit of God in you by accepting Jesus as your Lord and Saviour.