Networking in a symposium as a "non-specialist" I am going to participate to a symposium (or workshop or conference) for the second time. I am a PhD student and I'm not going to present anything there.

I know that networking is very important but I'm so bad at it! 
The first time I spent my time mostly with people of my group or directly involved in my project, and occasionally speaking with people I had met before once or twice (but almost exclusively when they were talking with the people of my group/project). 
In both cases the conversation was just small talk (I like this buffet, the weather is nice, there is a seminar next week at our institute) or was led by the other people, and I would intervene if directly involved or if I knew the technical topic well (e.g., I am using the same library, I had the same problem...)

I would like to try this so much praised networking, but I fear I will do just the same as before. I've seen the poster abstracts and there is only one directly related to my project, so I am afraid I will not be able to talk anything technical about other issues. I have a master in Engineering as do most of the other PhD students there, but we have different backgrounds and we have focused on different stuff in our research, so I don't feel talking about problems I have studied five years ago to people who have practiced on them until today. 
Is it expected to network as a "non-specialist"? I feel like that if I want to talk something to a fellow PhD student (not directly in a project similar to mine), it would be small talk and maybe the daily problems of a PhD student, but this seems like a poor alternative to me.
Let me tell you first that I can sympathise - networking also does not at all come natural to me. However, like most things, networking can be trained. The best opportunity to train is while doing it (or at least trying to), so your symposium should give you ample opportunity to improve.

First, if possible, do as JeffE says - have your advisor or some other (maybe more senior) person introduce you to people. Don't be embarrassed to talk about your ideas or your papers, or just about what you have learned during the symposium. That you come from a slightly different field may actually be an advantage here - the most interesting conversations I had at conferences often started with somebody saying "I, as an XY, find many of the presentations here really interesting, but why is there so much focus on A and so little work on B?".

Second, don't discard "small talk". Networking is mostly about connecting on a personal level anyway - it really does not matter so much what you talk about with people, as long as you talk to them. Talk to them about whatever comes naturally. It does not have to be about their research, even if this clearly is a natural conversation starter among researchers. Other standard conference convo topics (especially among PhD students) are: (1) life as a grad student, (2) difficulty with course work, (3) estimated time to graduation, (4) the ups and downs of the student's relationship with their advisor (although the last two bullets may be a bit loaded on occasion).

Third, try to not fall into the trap of seeing networking as "work", i.e., something that you'd rather avoid, but you know you need to do. This will make it automatically appear unpleasant, and you may end up just going through the motions so that you can say to yourself that you "networked", without achieving much.

Fourth, talk to people that you like talking to, and avoid like the plague people whose company you do not enjoy (for whatever reason). This sounds like a given, but I have seen many people classify conference participants into "important" and "unimportant", and then make a point to always talk to the "important" ones despite not actually enjoying it. This is a bad idea on multiple levels, including the fact that the PhD students from today are the professors and grant co-authors from tomorrow, so there really are no unimportant people in a conference.

Fifth, don't be too hard on yourself. You don't need to spend every minute of a conference networking. Many people, myself included, need a considerable amount of quiet time to function. Give it to yourself. It is ok to spend a few hours per conference day alone in front of your work, or on your hotel room if you feel tired of networking.

In the end, networking is the part of your work where the most important part is really to enjoy yourself. If you find one friend in the symposium, who you stay in touch with over the years, and who you write a grant proposal with in a few years, you networked successfully even if you talked to literally nobody else all week.