The eIDAS Regulation defines a simple electronic signature as: "the data in electronic format attached to other electronic data or logically associated with them that the signatory uses to sign". The simple electronic signature is usually the one where you request to accept a condition by completing a checkbox or an OTP code, and it does not have the ability to properly identify the signatory.
The eIDAS Regulation defines an advanced electronic signature as: "the electronic signature that meets the requirements set forth in article 26". The requirements in article 26 of the eIDAS Regulation are:
i) It is uniquely linked to the signatory.
ii) It is capable of identifying the signatory.
iii) It is created using electronic signature creation data that the signatory can, with a high level of confidence, use under his sole control.
iv) It is linked to the data signed therewith in such a way that any subsequent change in the data is detectable.
With the advanced electronic signature, the signatory has to draw their signature with their finger or mouse.
Although both electronic signatures have legal validity, the advanced electronic signature is more secure, as it obtains information to properly identify the signatory, and detect any subsequent change. Therefore, it's recommended to use the simple electronic signature when it's not vital to properly identify the signatory, and use the advanced electronic signature for documents or agreements that are sufficiently relevant, or where it is necessary to properly identify the signatory.