Now about قد , this word can be used as a verb or as a particle. (information to remember as well). Talking about it when it's a particle.
**** when we can use it ****
we use it to mean:
1. making sure about an action happened as well with no doubts.
for example: قد درست اللغة العربية I have been learning Arabic (means that you're sure about learning arabic in the past). Has a sense of " have been +ing" and note that after it, the verb is conjugated in the PAST!
2. when the verb after قد is conjugated in the PRESENT.
2.1 if you want to inform about something or someone in sense of "few, less, more". In otherwise, you want to inform your friend that he'll like something that HE CANNOT IMAGE, or about someone speaks a lot that HE CANNOT IMAGE : قد تعجبك المدينة كثيرا
قد يعلمك القليل فقط
2,2 about an action we aren't sure about, seems as "perhaps and maybe" as Mohamed gave you.
2.3 about something will be happened in the futur, and it is going to be happened soon. for example:
قد أقبل صديقي على الوصول إلى المنزل
++Note++ Sometimes we need to understand the meaning from the context at all. So, the important is done about the difference between " لقد and قد ,
salam