What is the basic difference between haram and makruh? When things became haram? And when became makruh?
When someone do a haram , he/she 'll be punished for that. (its a sin).
Doing makruh is not a sin, but not doing it will be awarded by God. (its preferred not to do it)
Etic speech: In this word there is no time for haram nor makrooh. we are born for Vajeb & mostahab. because time is limited. but after death is unlimited time. so how much value each second of life has?
Is there any way to know Why something is haram?
In shia the majority of scholars and professionals believes only Allah () and Prophet () and his Ahlol bait (a.s) knows the real reason of why things are haram or makrooh or...
so for one to know if X is haram or not, there is two way. he/she can read all the related ahadith & Quran and find out him/her self. or he/she can simply ask profesionals.
there are number of them I my self prefer ayatollah Sistani. (https://www.sistani.org/) they have an english site too.
but allow me to give you one secret key. most of the things which are against your wisdom are makruh or haram.
for example (Haram/makruh): being rude, eating too much food, forgettiing about neighbours problems/ discarding family relation ship / divorce (really makruh)
the problem is our wisdom is incomplete and it cant always give us an answer so its good to ask professionals and scholars to make sure you are right. but never forget to read hadith & Quran. may be at first we dont understand them much but after some time, they 'll become a very shining light in your heart that you can feel