Bhashya
योषा वाव गौतमाग्निः ।तस्या उपस्थ एव समित् , तेन हि सा पुत्राद्युत्पादनाय समिध्यते ।यदुपमन्त्रयते स धूमः, स्त्रीसम्भवादुपमन्त्रणस्य ।योनिरर्चिः, लोहितत्वात् ।यदन्तः करोति तेऽङ्गाराः, अग्निसम्बन्धात् ।अभिनन्दाः सुखलवाः विस्फुलिङ्गाः, क्षुद्रत्वात् ॥
In plain words
The woman herself is this fire, O Gautama. Her lap is the fuel, for it is through this that the fire is kindled to bring forth children. Her welcoming words are the smoke; her womb, the flame; the intimate acts within, the glowing embers. The brief flashes of joy are the flying sparks.
Close to the Sanskrit
The woman verily is the Gautama fire. Her lap is indeed the fuel; for by that she is kindled for the generation of sons etc. What she addresses lovingly is the smoke, from the arising of the woman of the invitation. The womb is the flame, due to redness. What she does inside, those are the embers, due to connection with fire. The joyous particles are the sparks, due to smallness.