FreeOffice: Creating and managing your own cell styles is not included in SoftMaker FreeOffice.
You can use the ribbon command Home | group Format | Cell styles 
to apply "Cell styles".
Cell styles are a combination of cell attributes (number format, orientation, borders, etc.) as well as the character format (font, etc.) that you can save. Once saved, all the attributes stored in that style are applied to the selected cells at once.
For example, if you want to frequently format cells with the number format "Percent", red background and bold font, simply create a corresponding cell style and apply it to as many cells as desired.
Note: In PlanMaker you can also apply character styles (see Character styles). The difference to cell styles is that character styles store the character format (font, etc.) only, whereas cell styles store both character format and cell format. Furthermore, character styles are also applicable to individual characters within a cell, while cell styles are applicable only to entire cells.
For more information, see the following pages.