The top part of the W4 form is a personal allowances worksheet that walks you through the process of stating whom you will claim as a dependent or if there will be no dependents.
You will separate that and keep it for your records.
The second half of the first page is the form that is submitted to the employer.
The employer might ask you to fill one out when you are first hired.
The second page has two different worksheets, the "Deductions and Adjustments Worksheet" and the "Two Earners- Multiple Jobs Worksheet.
There are income tables for Married and Filing Jointly and Others.
You can use form 1040es (download) for estimated tax for individuals and pay quarterly so that you aren't stuck with a big tax burden come tax time in April of the following year.
This link will refer you to www.1040-forms.com a good resource for info and printable forms.