There is an option to provide your Bitrix24 account address, please make sure you add account address in the correct format: e.g. mycompany.bitrix24.com, hola.bitrix24.es, etc.
Note that account address field should not contain @ sign.
In case you have social networks type of authorization, just click on the corresponding tab - Facebook, Google Plus or Vk.
If the system tells you that your login & password details are not correct, here is what can help:
- check your login & password combination in web browser
- make sure that you use correct login - check here Bitrix24 Network Profile
- you can always reset your password via this form
- if the system requests one time password after main login & password, this means your account administrator has enabled 2 step authorization for your account (read more about OTP here)