cant find disc 1 during installation

I'm following the installation guide to install sims 3 base game. I am at the point where it asks to insert disc 1 and I click browse but can't find it anywhere. Where would it be at/what am I doing wrong?

Also, if I install sims 3 now but want to install more expansion packs later will it still work or do I have to do them all at once?

Hello,

First, Mount both images. When the installation asks for Disk 1, click 'Browse' and select óne of the two Mounted Images. If you get an error, just click the other image you Mounted. When the Installation asks for Disk 2, do the same. The installation should go on now.
If you still don't understand the above, please watch our Installation Video on Youtube: https://www.youtube.com/watch?v=Dm1i-P4I7bc

The base game will work fine, as long as you follow the included "# Installation Guide.txt" file and do not update the game.
If you want to add more expansions afterwards, you must follow these instructions very carefully and DO NOT skip any steps: https://games4theworld.forumotion.com/t1171-must-read-how-to-install-the-sims-3-correctly

Good luck and please let us know if you need more assistance!