do you know html inline and block level tags
every tag which react like itself+br tag at the end it is block level tag
ol, ul etc.
inline tags are which shows inline and dont have br tag at the end
like b ,i ,u ,a ,strong, img ,sub, etc.
so in css you can cascade their properties you can make inline tag to block level tag and to block level tag to inline tag.
or you can show the as block and but show inline .inline-block is like they are blocks but floating to left.