From the Introduction to 6d6 Ultra-Lite
There is no right or wrong way to combine cards
In the 6d6 RPG, everything is done by combining different cards together to describe an action. For example, if character wants to hit a monster, they can combine their Brawn card and a Long Sword card. Or to convince a security guard to let them into a building, the Persuade and Quick Wits cards are played.
If a player wants to play an unusual combination of cards, they must explain why they think it makes sense. If the group agrees that it makes sense in this particular situation, the player can uses those cards.
User Summary of Basic Rules:
Players have small decks of cards, each of which describes a character ability. Character creation involves choosing a number of cards appropriate to their character, up to the limit imposed by the GM (for example, twelve cards).
When performing an action, the player chooses four cards relevant to that action and rolls 1d6 per card (modified by any additional rules as required). An action is successful is this roll exceeds the resistance (difficulty) of the action.