So, what constitutes an electronic signature? An electronic signature can be any method which can provide a way to identify the author of an online document - much like a pen in the offline world.
There are many ways for that, each comes with different complexity and reliability (protection against identity theft).
Among the easy electronic signature methods, we can find scanned signatures (or electronic representation of handwritten signatures) simply attached to the document.
While the more complex (and secure) methods can use certifications in the same way we secure our websites and bank transactions, thus providing an extra electronic signature verification.
There is also a possibility to include a representation of biometrical characteristics like a retina scan or fingerprint (of course these methods need special hardware on both ends of the communication and they're usually part of a bigger electronic signature service package).
In most cases, if an individual asked to electronically sign a document online, it will happen through an online electronic signature service, providing a secure way to store, validate and append that signature.
Why do we need e-signatures?
Since there are documents in the world, there are trust methods to make their origin identifiable - for businesses and even individuals it's usually important to reliably know who is on the other side of the messaging.
For physically existing documents it's an easy thing to achieve with adding a handwritten signature or a unique stamp of the organization.
However, since we're using more and more digital documents, which may never exist outside of the online world, it's becoming more and more important to apply the same reliability for them - that's why we use electronic signatures (also e-signatures or digital signatures).
What's the best electronic signature method?
It is important to note that for legal validity, a simple e-signature itself (like an attached scanned signature) is not always sufficient. For cases like that, you might need to choose a certified electronic signature service. Fortunately, you can find many services with detailed information about their capabilities.