Directly proportional means that if the terms on one side of an equation go up by a particular factor, then so do the terms on the other side increase by that factor. For example, if X and Y are directly proportional, then doubling X will see Y double as well.
Inversely proportional is the opposite, if X is doubled (ie multiplied by 2), then Y will be halved, effectively multiplied by 1 over 2. Whatever factor you multiply one term by, if another is inversely proportional to it, you divide it by the same factor (in this case 2).
Hope this helps!
PW