How do I register and apply for a solar pump on the PM-KUSUM portal?

There is no single all India apply button for PM-KUSUM. The scheme is run by your state nodal agency, which is usually the state renewable energy development agency, and in many states the DISCOM or the agriculture or horticulture department handles part of it. So the right place to apply is your own state PM-KUSUM portal, not a random national link. The usual flow is: open the state portal when the application window is live, register with your mobile number and Aadhaar, fill in your district, village, land details, and the pump capacity you want, and upload the documents the portal lists. Common documents are Aadhaar, a land record such as 7/12 or khasra khatauni or RoR, a bank passbook for the subsidy transfer and refunds, a passport photo, and in many states a water source or borewell proof and an existing electricity connection declaration so they know whether you fall under the off grid Component B or the grid connected Component C. After you submit you get an application number, the agency screens it, and if selected you get a demand note to pay your farmer share. Only after that does an empanelled vendor get assigned. The portal name, the live or closed status of the window, and the exact document list differ by state and change every season, so confirm the current portal address and document list with your state nodal agency before applying.