my psd file is 9900px by 6600px and I want to export it to jpeg for a website. When I try to export it to jpeg with 72ppi and lower down pixel dimensions to about 1000px by 750px, the image comes out pixelated. It's so frustrating, please help.
In Photoshop the best option for saving a single image for output to a website is the
Save For Web tool.
This allows you to set up your PSD for export to JPG and gives you options to take care of the resizing, resampling and conversion to sRGB which is a good idea for the web. Also the tool allows you to look at samples of the image and decide which quality level is going to give the best size/quality tradeoff for screen.
Don't change the resolution of the image. The resolution is irrelevant when you display images in a web page. The browser only cares about the pixel dimensions of the image.
Just resize the image to the pixel dimensions that you want.
If you then want to set the resolution (although the browser doesn't care), use the Image Size settings again, but uncheck the Resample Image option so that it only changes the resolution setting without resizing the actual image.
After resizing you might want to gently use the Unsharp Mask filter. I generally use settings like: Amount: 50, Radius: 0.5, Threshold: 2.
Then you can export as JPEG. If you don't use the sRGB color space already you can use the option to convert to sRGB. No need to embed a color profile.