3.2Your first transformation

Input:

{
  "customerId": "12345",
  "companyName": "Acme",
  "phone": "305-555-1234"
}

DataWeave:

%dw 2.0
output application/json
---
{
    id: payload.customerId,
    name: payload.companyName,
    telephone: payload.phone
}

Output:

{
  "id": "12345",
  "name": "Acme",
  "telephone": "305-555-1234"
}

This is your bread-and-butter Salesforce mapping.