The easiest way is to send me a compressed folder containing the audio files from your song. Please make sure that all of your audio files were exported from the same starting point. These files should be in the same sample rate and bit depth as your session (usually 44.1 kHz and 24-bit).
Here’s an article from soundbetter.com that can help you prepare your tracks for mixing. I also recommend checking out The Pro Audio Files and their 9 Tips for Preparing a Session for Mixing guide.