Islam in its general sense refer to worshiping Allah (or God and same God in Judaism and Christianity) as the one God and only one God with no partner, no companion, no son, no father, no associate, and no equivalence.
The key beliefs are the Islam five pillars (refer to related question below). Refer to question below for the Islam main fundamentals.
Islam is a religion not a country. Refer to question below.
Islam never spread by war. Refer to question below.
Islam means full submission and surrender to God will. Refer to question below.
Islam religion was originated by start of universe creation. Refer to related questions below.
Sure, there are Christians who converted to Islam. Refer to the link below.
It is the action of being adhered to Islam fundamentals. refer to question below.
They are five Islam pillars and not three. Refer to related question below.
There is no Patriarch for Islam. Allah (or God in English) is the founder for Islam. Refer to related question below.
Islam is not something lost to be found. I think the question is who founded or established Islam. Accordingly, Allah (or God in English) founded Islam. Refer to question below.
If you mean by the word " things" the fundamentals or morals of Islam, then refer to questions below
It is Islam since start of universe creation. Refer to question below.