Sure, here's a step-by-step guide on how to make a big Spotify playlist:

1. Open the Spotify app on your device.
2. Click on the "Library" option located at the bottom of the screen.
3. In the library, you'll see an option for "Playlists" at the top of the screen. Click on that.
4. You'll then see a button that says "Create Playlist". Click on it.
5. You will be prompted to give your playlist a name. Type in whatever you want to call your playlist and then click "Create".
6. Now that your playlist is created, you can start adding songs. To do this, go to the song you want to add, click on the three dots next to the song, and then select "Add to Playlist".
7. A list of your playlists will appear. Select the playlist you want to add the song to.
8. Repeat steps 6 and 7 for each song you want to add to your playlist.

Remember, there's no limit to the number of songs you can add to a playlist on Spotify. You can make your playlist as big as you want. Enjoy your music!