It is important for you to make sure your wallet is synced before you log in, send coins, and create addresses, especially when using light wallet which may be not always synced. You can't properly operate the wallet if it is not synced and IOTA's syncing is different from blockchain coins.
Check the milestoneindex and solidsubtanglemilestoneindex in the View Node Info under Tools. If these two numbers are same and equal to the latest milestone number in #botbox on Slack, your wallet is synced.
You also can simply check the Status Bar (if you have made status bar visible) on the bottom left of your wallet. If the first two numbers are same and equal to the latest milestone number in #botbox on IOTA Slack, your wallet is synced. Otherwise it is not.