For a website, you need somewhere to host it. The ISP you use for your internet connection may be able to provide that but if not, there are plenty of companies out there that do it. Prices vary and to some extent you get what you pay for. the cheaper / free options tend to restrict how you present your website and may carry advertising etc. you have no control over. The better providers offer more flexibility and control. A reasonable yearly cost would be under £100 per year.
Second thing you will need is a domain name. Some hosting packages include one for free, others charge separately. These days there are lots of extensions (.com, .co.uk etc.) to choose from so choose wisely!
Once you have your host and domain, you need to build a website. If you know a little about this, you could do it yourself and perhaps use one of the site builders most ISPs offer. Again, there are many alternatives. I created the AWGB websites with Wordpress. This is widely used and supported with many plugins to add functionality as required.
If you are going to sell online, you really need to make your site secure so you would need to have an SSL certificate. These may cost another £50 per year. Some are more, some are less.
If you need to employ a specialist to build your website for you, make sure the whole thing is kept under your control and that you have full administrative access both before, during and after the work is done! Also make sure you have a contract that sets out what you are paying for and what the costs are and don't hand over any money until the contract is fulfilled to your satisfaction.
A word of caution - there are plenty of unscrupulous companies out there who will promise you the earth and deliver a pot plant so choose carefully! I know of more than one person who either got burnt or had their website hijacked by their web designer due to a dispute and the last thing you want is the website you have been promoting to have a big banner calling you a cheapskate or worse! Yes these things can be taken down but by then the damage is done!
For Facebook, go to the site and follow their instructions for creating a "fan page" rather than using a personal account. If you do the latter and become moderately successful, at some point, they will spot it and force you to switch so save yourself the pain! They say more than 20% of the world's population uses Facebook so the potential market is huge. Unfortunately FB deliberately throttle the number of people who see what you put on there. Then they charge you money to increase the viewings. Effectively you are paying them for your hard work