You can purchase tub butter, butter sticks, margarine blocks.
Tub butter/marg is soft and spreadable.
You can spread it on toast or use it to grease a pan, but it’s unsuitable as a baking ingredient because it contains additives which affect melting temperature, causing recipes to yield unexpected results.
However, churned butter sticks and margarine blocks are optimized for baking, they come in individually wrapped, pre-measured portions; 1/2C or 8 TBSP, with each tablespoon being marked on the wrapper making it easy to cut off the portion you need.
Churned butter comes in salted and unsalted, I always use unsalted since most baking recipes contain salt anyway and I don’t want any of my ingredients to already contain salt.
When making pastry always use cold butter, read here for more info on butter temperature.