To encrypt a file or folder with 7Zip, install 7Zip then right click a folder and select Add to archive. To encrypt the files, you will have to add a password. Input the password two times and then choose the Encryption protocol. For the 7Z archive you can choose AES-256 encryption protocol which is the highest and the recommended one to be used. You also have the possibility of encrypting file names. To do this, check the Encrypt file names option.
To see how the Add to archive image appears, use the following image: