The key to finding the death certificates lies in the indexes to the deaths. If you have a death in Los Angeles county in 1958, look for the 1958 index to deaths and find the name of the deceased in that. It will give the certificate number. Then go to the link for the 1958 deaths that contains the range of numbers your death certificate will be in.
For example: I'm looking for Jane Doe who died in Los Angeles in 1958. That's all the information I have. I use the link I posted in my offer above, find the index of 1958 deaths, since they're arranged alphabetically, I find Jane Doe in the D's and find her certificate number is 10801. I then go to the list of all records, find the 1958 death certificates that go from 8001 to 12004. I've gotten pretty good at guessing where in the image range certificate number 10801 will be. The image number is not the same as the certificate number. In the certificates that start at 8001 and go to 12004, there are 2500 images. I will start at image 1000, see what certificate number that image is and then go from there either forward or backward in image numbers to find the image number that shows certificate 10801. (These are examples, not real numbers. I'm too lazy to look up the actual image and certificate numbers. This is just an example to show how you'd find a death certificate for a fictional Jane Doe.) I hope this helps.