Gardenscapes-New Acres splits it's garden-building simulation into many small tasks spread across multiple days. As you complete tasks, the percentage bar for the current day will fill up. Once you complete the last task for that day, you will reach 100%, receive a reward and you will be able to start a new day. Starting a new day completely refills your energy bar up to 5 lives, so it's best to wait until you are out of lives to move on to the next day.
In order to complete garden tasks (missions) like installing benches, fixing the treehouse etc., you will need to spend stars. Stars are only earned when winning match-3 levels- one star per completed level. Although you can spend your stars as soon as you get them since you always have a mission on deck, you can also save up and complete a lot of missions in a row for a faster sense of progress. Technically, you don't have to fix the garden at all- you could just play match-3 levels and earn stars, but then never use those stars to help Austin rebuild the estate, but where's the fun in that?