Humans are motivated by rewards. In the same way that adults are motivated by rewards, be they tangible or intangible, children are motivated by rewards as well!
Let’s differentiate between a "reward" and a "bribe." Rewards are motivating and push children to WANT to achieve their goal. Rewards are initially set up, before the new routine/expectations are presented and expected. Bribes are usually spontaneously decided on when a bad behavior is happening and you're desperate. ("If you stop throwing your food, you'll get a cookie!")
Depending on what your child is working towards, pick a reward chart with either 3, 4 or 5 squares. I recommend using a 3 square reward chart for younger children (ages 3 and 4). However, you can still use them with 5 and 6 year olds. Start small and work your way up to the reward charts with 4 and 5 squares.
Like most things, reward charts are only effective if the adult follows through and is consistent with them. If you want the child to succeed, it will require some patience, enthusiasm, and follow through on your end. You can do it! Stick with it and you'll see the results you're looking for.