Kami is not translated well by "god". The word covers the powers of striking places and things (a waterfall, an old tree, a rock, a mountain, a storm), as well as ancestors, the dead of a locality, historical figures, and abstractions such as growth or the harvest. Some kami are known across the country and appear in the eighth-century court chronicles; most are local, tied to one shrine and one community, and have no mythology at all beyond being there.
A jinja is the kami's residence rather than a hall for congregational worship. The visitor passes a torii, which marks the boundary between ordinary and sacred ground, rinses mouth and hands at a water basin, and makes an offering with a bow, two claps and a bow at the outer hall. The inner sanctuary holds an object in which the kami is understood to be present and is not open, in some cases not even to most of the priesthood.
The organising concern is purity rather than sin. Pollution is contracted from death, blood, illness and disorder, and is removed by washing, by salt, and by the priest's purification rite. It is a condition, not a moral fault, and it is treated by cleaning rather than by repentance. This is why Shinto handles birth, marriage, new buildings, new cars and new businesses, while funerals in Japan are overwhelmingly Buddhist.
Festivals, matsuri, are the tradition at its most visible: the kami is invited into a portable shrine and carried through the district it protects, with music, food stalls, drinking and crowds. The atmosphere is closer to a fair than to a service, which is a fair reflection of what the occasion is for.
There is no creed to assent to and no membership to take up. Participation is what there is, and it is generally understood as belonging to a place and its community rather than as a statement about belief.