Open up the Nuendo project you wish to mix. If you wish to build a new project with audio files recorded in another DAW, create a new project by selecting "New Project" in the "File" menu, choose the template "Empty" and select or create a folder for any new audio to be recorded to. Then import your audio files by dragging them into the project window.
Assign tracks to the desired output. To do this, select each track in the Track List, then in the far left column, called the Inspector, find the row that begins with what looks like a left bracket and an arrow pointing right. Click on this row and assign the track to an output (for basic stereo mixing, it's usually "Stereo Out").
Add folder tracks to your project by selecting the "Add Track" menu in the "Project" menu. Then select and drag similar tracks, such as all of the percussion tracks or vocal tracks, into individual folders. This will reduce visual clutter in the project window, as each folder can be expanded or collapsed.
Select a particular instrument(s) to build your mix around and mute all other tracks by clicking the "M" button on those tracks in the Track List. Press the play button on the transport controls to begin playback and ensure only the desired tracks are heard. It's common practice to start with the percussion or bass instruments.
Select the "Equalizers" tab in the Inspector for the track you're mixing. Enable the equalizers you wish to use by clicking on the "Power On" symbol in the upper left of each equalizer and adjust the parameters (top to bottom: gain, frequency and bandwidth) to taste for the particular track you're mixing.
Select the "Inserts" tab in the Inspector of the same track and click in one of the blank rows below. Navigate through the list of plugins and add as needed. Under default project settings, each channel may contain up to eight plugins.
Open up the Mixer by selecting it through the "Devices" menu or by pressing F3. Use only the middle section of the mixer to manipulate active track settings, and set the track level with the fader and the pan position with the horizontal bar just above the fader.
Unmute the next track you wish to add to the mix by clicking on the "M" button on its track and adjusting its individual EQ, plugin, pan and fader levels. Repeat with each track until all are unmuted and audible in the mix.
Set the left and right locators to highlight the area on the timeline you wish to export to a single audio file. To set the left locator, set the cursor in the desired location and press control (command on Mac) and 1. To set the right locator, set the cursor in the desired location and press control (command on Mac) and 2.
Export your mix by clicking on the "File" menu, highlighting "Export" and then selecting "Audio Mixdown." This opens up a dialog box asking you to specify the file name, file destination, file format and audio engine output. Adjust these settings as needed, making sure that the output is the same as the output of the tracks you're mixing down.