بسم الله الرحمن الرحيم
Ghusl becomes fardh after having intercourse with wife. Whether transparent liquid substance like water discharges before ghusl or not; ghusl is wajib on you in all conditions. But if you did foreplay only and did not penetrate your penis into the vagina of your wife and the liquid substance like water discharged due to foreplay then it is madhi and it does not make ghusl wajib. It is enough to wash the private part and the place where the madhi is smeared. You may offer salah after washing and making wudhu. If you pass urine before making wudhu then it is better as it shall clear the drops of madhi which remained in the urinal passage. If underwear is smeared with madhi then it shall turn pure if you wash that part. If your pant is not smeared with madhi then it is not wajib to wash it merely due to doubt and supposition.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.