Where to sign the 1040 and do I have to fill everything down?(fron page 9 to page 12 on the pdf file)

You use a pen to sign a Form 1040 next to the big black words that say "

Sign here.

"  If you are filing a joint return with a spouse, then each of you signs the form.   And you enter the date.

If you are printing the tax return for mailing instead of e-filing, then you sign and date the federal tax return, Form 1040 on page 2 of the form in the Signature block provided

Include with the Form 1040 all other forms and schedules which have an Attachment Sequence Number located in the upper right corner of the form or schedule.

If you are e-filing your return, there is no physical signature.   When you e-file, you "sign" electronically by entering your AGI.