If you look at the very beginning of the novel, one of the symbols is the lighthouse itself. Because of the fact that it is solid and unchanging, unlike the weather (which the father is particularly concerned with) it can act as a goal, something for people to reach out to in the midst of so many of life's uncertainties.
Another symbol, in some ways, is the marriage of Mr. and Mrs. Ramsay as it mirrors that of Woolf's parents own marriage. Their respect for each other's ambitions as well as the particular cares they have about certain issues is well evidenced and is very similar to the reputation of Woolf's parents.
For the concerns and themes of the novel, the guide below is fantastic, but one of the main ones, as in most literature about that time, is the impact of WWI on not only the political and economic climate but also the psyche of the characters themselves.