How to send files using discord.py?

How do I send files using discord.py? Here is my code:

import discord
from discord import app_commands
from discord.ext import commands
import random

TOKEN = "" # my token

bot = commands.Bot(command_prefix = "/", intents = discord.Intents.all())

@bot.event
async def on_ready():
    print("Bot is Up and Ready!")
    try:
        synced = await bot.tree.sync()
        print(f"Synced {len(synced)} command(s)!")
    except Exception as e:
        print(e)

@bot.tree.command(name = "roll", description = "roll a dice!")
async def roll(interaction: discord.Interaction):
    await interaction.response.send_message(f"`{random.randint(1, 6)}`")

so far I only made a simple command that rolls a dice. If for example, I have a file named song.mp3 in my root directory, and I want to upload (send it) in a slash command, how do I do that? I want something like this:

@bot.tree.command(name = "song", description = "send the song")
async def song(interaction: discord.Interaction):
    await interaction.response.send_message(f"{the_song_file}")

I want to like how when you drag and drop a file into discord chat to send it, but I want my bot to do it.

You're on the right track using the send_message method.
The same method can send a file when given one:
Looking through the documentation, we see a file parameter, which we can use:

@bot.tree.command(name = "song", description = "send the song")
async def song(interaction: discord.Interaction):
    await interaction.response.send_message(file=discord.File(file_to_send))

Note that you have to open the file before sending it using discord.File, instead of sending the file's path.