Cryptocurrencies are built upon a cryptographic system, a system that makes use of pairs of keys: public key and private key. The public key: essential for identification and receiving funds, can be made public and the private keys: essential for Authentication and encrypting data, should be kept secret.
The technology behind this cryptography is very sophisticated and cannot be easily explained,however we will try to make you understand in the shortest way possible. When you sign up to a cryptocurrency, a public address and a private key is generated for you, the address is used for sending and receiving funds and also holds your balance. While the private key authenticate any transactions that is about to be made out of that particular address. Without the signature of the private key no transaction can be made as there is no proof ownership. In simple term, private key is what grants you ownership of funds in an address.
No, actually the address is a shorter form of your public key also the public key is derived from you private key and the process cannot done in reverse order, meaning the private key cannot be derived from the public key and public key cannot be derived from the address.Your unique private key is the only thing that can be used to authenticate any transaction you make, so if anyone other than you have access to it then they also have access to your funds, it is thereby very important to keep your private keys as safe as possible and away from prying eyes.
Once you lost your private key, then all funds and access to it has been lost also, there are no mean to recover them, so your funds are lost for life!.
Technology has eventually made that quite easy as Blockchain and most Digital wallet app will not disclose your private key to you nor anyone else but rather store the key and allow the software to sign any transactions that is about to be made with the private key. It is an automated process so you don’t have to worry about hiding or losing your private key.