We recommend that you exercise caution when giving your login credentials to anybody. Steps you should take include:
Give your expert admin access to your account
This is the safest option as your expert will have their own login credentials to your account. Find your app in this list of instructions for more specifics. You will also receive these instructions in your confirmation email.
Don't give your personal login credentials
Most platforms offer the ability to add admins to your account, so there's no need to give out your personal username or password to your expert. If you're getting help on a desktop application (like Adobe Photoshop), then you can just share your screen for the session.