You can think of LinkedIn as a professional version of Facebook. It is where you make professional connections rather than social connections. It is not the place to share what you had for breakfast! (historical note - that expression comes from the early days of Twitter where people didn't see value in reading about what others had for breakfast).
Since I have had several jobs, I use LinkedIn as a way to stay in touch with people that I have worked with in past jobs. My first manager is connected to me on LinkedIn - without that connection we would have lost touch. I actually started on LinkedIn when a colleague in my Master's program invited me to connect. It was a brand new platform at that point.
When I returned from our 16-month bike trip and was looking for work, I posted a message on my LinkedIn status saying "I'm looking for work", and someone from a previous job reached out to me with a job opportunity that I otherwise would not have found. I ended up getting the job and was back at work within a month of our return - in a job market that was taking people on average 6-months to find a job. It was letting my network know I was looking, that helped me land that job.
I recommend that everyone have at least a minimum profile on LinkedIn, and that you use it to connect with your colleagues. If you don't need it now, you may find that you need it at some point in the future - and when you need it, it is often too late to start. You can add your new website to your LinkedIn profile. If you make a blog post that your network might be interested in, you can post it to your linked in status. This let's people in your network see your post. I don't do this that often - as I don't want to overwhelm my network, but if I write something that I'm particularly proud of I do broadcast it there. This practice of posting content to LinkedIn is becoming more common.
If you want to grow your network outside of the people you already know, then joining LinkedIn groups is a good way. One way to do this is to search for several LinkedIn groups and join them. Watch the group for a while to get a sense of what people are posting. When you have something to contribute, jump in and add your thoughts. When others see them, they may want to connect with you.
Think about who you want to connect with and who you don't. I generally try to avoid accepting connection requests from people I don't know. When sending a connection request, it is a good practice to tell the person how you know them (unless you are close friends or colleagues). For example, I meet a lot of people at conferences. If you don't tell me you met me from the conference, I may not accept the invitation because I don't know who that person is.
If you have access to LinkedIn Learning, there is a great course called Rocking your LinkedIn profile. One nice thing about this course is that it is regularly updated as new functionality becomes available on LinkedIn. I recommend reviewing it at least twice per year.
Joining a LinkedIn group is a great way to connect to professionals in fields that you are interested in. In addition, it is a great way to share your ideas and thoughts on topics of interest. Remember that LinkedIn is a professional social media platform. This is not the platform to be sharing your vacation photos. I highly recommend lurking (reading/following) the LinkedIn groups for a while before posting to them - that way you get a better sense of the type of things that are shared within the groups.