- Open up your Steam client and choose View, then click Settings
- Choose Interface and check the box that reads, "Display Steam URL address when available"
- Click OK
- Now click on your Steam Profile Name and select View Profile
Your SteamID will be listed in the URL at the top left (it's the long number at the end.)
If you have a custom URL, the number will not be listed. In that case, just give us the entire URL.