@sal19515 You should have received an employer nomination form signed by the company representative, indicating the job title, job description, expected remuneration and other terms and conditions. You will need to sign that form and attach a copy of your passport and those of your dependent(s), if any, as well as other documents that may be required.
After signing and attaching required documents, you will send this back to your employer or his/her representative, which could be the migration agent, who will submit/lodge the nomination for the Department of Home Affairs. You can either wait for the approval of the nomination or if advised to do so, lodge your visa application online using the immi system. In some instances, the migration agent can also do this for you depending on what has been agreed between him/her and your prospective employer.
If you will be lodging the visa application yourself, you will be given a Transaction Reference Number or Application Number which you need to input in the system to be able to proceed with your visa application.