Lube is a liquid that is used to keep your drivetrain (i.e. chain, rear cassette and front chain rings or crank/chainset) running smoothly. While it’s okay to wash your bike with washing up liquid rather than a specific bike cleaner, nothing should replace lube. A chain that sounds like you have field mice nesting in it is not good. This little bottle of liquid will prevent this and help to prolong the life of these components.
If you’re using your bike every day to commute then washing it after every ride may not be practical, but at the very least you should clean, dry and lube your chain and cassette. Doing this will only take five minutes or so and will prolong the life of these parts.
On a daily basis use a spray based lubricant like GT85. It will help to disperse any water in the chain and keep it running smoothly, be careful not to get any onto braking surfaces. Use a rag to dry off your chain and between the cogs on your rear cassette, then spray some lube onto the chain, turn the pedals and as you do so change up and down your rear gears allowing the chain to move up and down the cassette distributing the spray. Wipe off any excess with a cloth.
On a weekly basis give your chain a more thorough clean and use some specific chain lube dotting it onto the chain in the manner described previously. Lube comes in a few different guises depending on the conditions you are riding in, as a general rule of thumb wet lube should be used in winter and dry in summer.