My baby cries when I put him in the sling

This can happen - especially if you are still unsure about tying the sling. With time, tying and adjusting the carrier happens very quickly and the child gets used to the process. Some parents also sway or move around while tying, which can defuse and distract from the situation.
But you will see: As a rule, your baby will calm down as soon as he or she is tied and you start moving.