The initial dissatisfaction many people feel towards determinism may be largely due to their conflating it with a notions of pre-destination, fate, or destiny. I want to take this opportunity to highlight the differences, and so assuage some of the common concerns about freedom & determinism. The key differences are in regard to the 'overall purpose of things', and - most importantly - the impact of individual strivings & contributions to history.
First, the notion of 'purpose'. I simply want to emphasise that determinism has none. Those other quasi-religious notions are all built around the idea of events leading up to some inevitable goal which must be realised no matter what. Determinism, by contrast, has no inherent goals, it's just the way things are. Sure, it means that future states are inevitable given the past states and the laws of nature, but there is no personal driving force behind it all, no God or gods imposing their will upon us hapless mortals. I think that's an important distinction to bear in mind.
Most important of all, of course, is the question of an individual's power to contribute to the shaping of history. According to 'destiny' notions, there is a fixed (divine) goal which will be attained no matter how much we strive against it. Human actions don't make any difference - fate ensures the future will turn out the same no matter what we choose or how we act. The phrase "you can't fight fate" pretty much sums it up.
Our cultural heritage has tied 'determinism' and 'destiny' notions very closely together. This makes it a difficult link to break, though for purely psychological reasons. For hard though it may be for us to see (at first, anyway), the gulf between these notions is vast indeed.
The key difference is that while destiny excludes us from influencing the future, determinism does quite the opposite - in fact, it needs us to shape the future. This is best demonstrated hypothetically: suppose you die in a car crash tomorrow. Now, according to 'destiny' notions (e.g. suppose you are destined to die tomorrow), then even if you avoided cars altogether, fate would nevertheless contrive some way to kill you off. Maybe you'd get struck by lightning, or have a heart attack, whatever. Contrast this with determinism: if (contrary to fact) you had avoided cars altogether, then you would not have died that day at all. Your different actions would cause all sorts of different consequences - perhaps you would go on to cure cancer and live to see 100!
You may think these hypotheticals irrelevant - "what matters is reality, and in reality it's determined that I die in a car crash tomorrow and there's nothing I can do about it!". This complaint sounds plausible, because there is a sense in which it is literally true. But it's also severely mistaken due to a conceptual confusion about the nature of control.
You lack control if your actions lack causal power, i.e. if no matter how you act, the future will not be affected. Hypotheticals are thus central to the notion of control; to assess whether you have control or not, simply look at those (hypothetical) possibilities where you act differently, and see if a different state of affairs results. According to destiny, it won't. But according to determinism, it will.
Your actions determine the future. That is the way to understand determinism without making the all-too-easy mistake of conflating it with destiny notions. It is also the case that "past events determine your actions", but we are in a far worse position to understand the true nature and implications of that proposition, so if you focus on it too much (as people commonly do), then misunderstandings of determinism will inevitably result.
The heart of the matter is that destiny notions deprive us of a place in history. They imply that the same future would result with or without us - they exclude us from the causal chain. Determinism, by contrast, embeds us deeply within the causal chain. Sure, other stuff makes us happen. But then we make things happen. Without us, they would not. If we acted differently, things would turn out differently. Of course it is true that in reality we don't act differently - we act the way we do. But that doesn't mean our actions don't have consequences. It doesn't mean that we are excluded from the causal chain. It doesn't mean that we don't shape history.
It is commonly believed that determinism implies we lack control over our lives. This couldn't be further from the truth. Determinism not only co-exists with personal freedom, but indeed, by embedding us within the causal chain, it provides our freedom.