I upgrade to yosemite but I can't use aperture

You probably need to upgrade iPhoto first:

Get iPhoto 9.6.1 if you didn't update before OS... | Apple Support Communities

Cheers,

GB

In 10.10.3 the Aperture and iPhoto applications were superseded by Photos.

10.10.3 is the Yosemite OSx version. The version of iPhoto that is compatible with 10.10.3 is 9.6....

GB

Which version of Aperture do you have? Was it a retail version?

If you associated it with your app store before Yosemite, then there was an update available and it will run in Yosemite - I am running v. 3.6 in 10.10.4.

Aperture runs well in Yosemite; it was discontinued, not superseded.