TikTok allows you to use a basic two-factor authentication method. To keep your account secure you really should enable this:
TikTok has a lot of controls on who can see your account, your content and your activity. We strongly recommend that you take a good look at these, and consider making your profile private if possible.
TikTok heavily personalizes the ads shown to you. Under Privacy -> Ads personalization you can (and should) disable this: