If you are looking into hosting for your website then you have a few options. Historically it used to be shared servers or dedicated servers but you can often now opt for a cloud server package as instead if you wish. All of the different types of servers have advantages and disadvantages and often your choice will mostly come down to cost. Dedicated servers are usually the most reliable and allow you to have complete control over how they are run.
If you decide that you cannot afford the monthly or annual fee of a dedicated server for your website (which can often be in the region of £100-£300 per month) then you will probably have to settle for a shared server.
A shared server means that not only will your websites be hosted on there but also potentially hundreds of others that you have no control over. Usually, this will not cause a problem but if one of the other websites causes an issue such as overloading the server, you will find that your websites will also be affected and go offline. If the shared server IP address gets blacklisted as one of the domains is sending out a lot of spam, then you may find that your genuine emails also start to be rejected by many recipients. This can also have an effect on your rankings on the search engine if you IP is thought to not be safe.