SSL (Secure Socket Layer) certificates encrypt data between the server and the viewer, this is especially a good idea if you have an online shop and accept direct payments. Also apparently Google now gives extra recognition to sites with SSL certificates.
123host offers free Let's Encrypt SSL certificates to all customers, but this only works if you use https:// instead of http://. If you use WordPress it can be helpful to install the Really Simple SSL plugin which makes SSL easy....and simple ;o)
Certificates last for 90 days and renewal is automatic in the background.
Your certificate will be attempted to be renewed every day starting 30 days prior to it expiring.