If you envision the political spectrum as a bar, the range for leftist would be on the far left edge, while the range for liberal would be around slight left-of-center to center. This isn't only exclusive to US politics, but they would be the most prime example of how jarring the gaps between the various ideologies are.

The easiest way to compare the difference without getting into any policy jargon is in mindset.

The core of liberalism is being pro status-quo. The system is broken but it just needs some fixing. They don't believe in drastic action even in times of desperation. There's a secret 3rd way to solve a problem, and if there are two bad options then just choose the lesser evil and don't question it.

While the leftist sees the system as something that functions the way it was intended to by the puppetmasters, and as a fiend that's necessary to destroy. Dismantle the contributing factors that govern us. Perhaps this is oversimplified, but I hope it gets the point across.