When you encounter a Jelly Level in Candy Crush Saga, you'll need to remove all the jelly blocks before you can complete the board. You'll need to make a match over the Jelly's square. Some Jellies need one match to destroy them while others require two. It can be kind of difficult to tell the two types apart, especially if you have poor eyesight like I do. The blocks that need two matches are whiter and more solid looking. The transparent jelly blocks only need one match.
Keep yourself focused on these boards and remember the goal of the board is to remove all the jelly blocks while still racking up enough points to complete the level. Watch out for Jelly blocks that are on the top of the board and squirreled away on the side corners as these can be challenging to remove.
Timed levels are just what they sound like... levels that need to be completed within a certain time period. Focus on making high impact matches of 4 or more and use your special candies to ensure you quickly rack up your score before time runs out. You'll also see special candies with a +5 on them. When you make a match with there, you'll add 5 seconds to the clock.
Ingredient levels will feature special ingredients that you will need to move to the bottom of the board by making matches and letting the ingredients quickly fall. Remember to focus on the ingredients in these boards! Not all the ingredients will be on the board when you start. You'll need to keep making matches to bring them down into the playing field.