mandar vs enviar
Both mean 'to send'. Enviar is neutral and a touch formal; mandar is common in speech and also means 'to order'.
enviar
To send — letters, emails, packages, people.
Te envío el archivo por correo.
I'm sending you the file by email.
Slightly formal. Common in writing.
Enviaron un paquete a mi casa.
They sent a package to my house.
Postal and delivery contexts.
Han enviado a un enviado especial.
They have sent a special envoy.
Sending a person on a mission. Enviado = envoy.
mandar
To send in everyday speech, and to order or be in charge.
Mándame un mensaje.
Send me a message.
Casual, spoken. Very common in Latin America.
Mandó a su hijo a la tienda.
She sent her son to the shop.
Mandar a + person + a + place.
Aquí manda mi madre.
My mum is the boss here.
Mandar = to be in command. '¿Mande?' in Mexico = pardon?
Tricky bit
'Mandar a alguien a paseo' / 'mandar a freír espárragos' = to tell someone to get lost. Mandar covers more idioms than enviar.