There are three trading offerings on dYdX: Spot, Margin and Perpetuals.
To trade on dYdX, users must first deposit funds into their relevant account. On dYdX, you have your Spot account, Margin account, and then a separate account for each Perpetual. Offering portfolio margining across these products is something the team will be looking into in the future.
dYdX offers three spot markets: ETH-DAI, ETH-USDC and DAI-USDC. Once on the Spot tab, you can trade freely using market, limit and stop orders.
dYdX offers margin trading on the same three spot markets with up to 5x leverage. Margin trading can be accessed on the Margin tab, where you choose either the 'Isolated' or 'Cross' mode on the trading sidebar. Here is a great place to start if you're getting started. https://medium.com/dydxderivatives/getting-started-with-dydx-margin-trading-part-1-fe43789c2368
dYdX offers Perpetual Contract Markets that allow up to 10x leverage on synthetic assets with no expiry. dYdX offers three perpetual markets: BTC-USD, ETH-USD, and LINK-USD. All Perpetual markets are listed on the Perpetuals tab.