You can introduce solids any time between 4 months to 6 months if your baby is ready.
Cues to look for if your baby is ready for solids:
*Head control. Your baby needs to be able to keep his head in a steady upright position.
*To keep solid food in his mouth and then swallow it.
*Sitting well whe supported.
*Your baby's mouth and tongue develop in sync with his digestive system.
Like what Yuna has shared, you can start off with fruits and vegetables purees that contains water.