Help! I can not get into my iPhoto since I upgraded my computer. I have thousand pf pictures on there!

iPhoto was discontinued 5 years ago. It is no longer developed or sold. It was replaced by the more powerful (and free) Photos.app that comes with the OS. You can migrate to that app very simply:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.

If you prefer not to use Photos there are several 3rd party apps that you can use. Which to choose depends on the kind of photographer you are and your budget.

Photos is your best bet, and the price is right.

as I have now lost options of opening older files from 10 years ago

there is no reason why this should have happened. Can you explain more?

Ideally I would love to have it all put in a file that can be in order of dates, month and years

You can do that in the Finder yourself and just not use Photos at all. However, it will make finding your photos more difficult.

Some questions:

1. What kind of photographer are you? By that I mean are you a family diaper, taking photos with your phone or point and shoot camera on vacations or at family events? Or a serious hobbyist? Are you shooting Raw or Jpeg? Using a DSLR or Mirrorless? Or, indeed, a pro?
2. What's your budget?
3. What features do you want? Or is there anything about the apps you use now that you dislike?

I'm just taking photos point and shoot. grabbing memories not looking to win awards with my photo skills. I just want to be able to transfer my photos from phone to the Mac but I hate how they keep changing iPhoto/photo with upgrades as I have now lost options of opening older files from 10 years ago. Ideally I would love to have it all put in a file that can be in order of dates, month and years

HI I would love to know what 3rd party apps you know of as I have been looking and not sure what to go for.

I have been using iPhoto, and now Photos from the beginning, and have never lost access to my photos. The trick is to stay up-to-date on your software.