If you decided that you wanted to try a church or try a new church in a totally different denomination, you know you would be able to slip into a pew and not be noticed. Either that or there's a welcome committee ready with brochures about their church. A lot of Protestant churches hand out programs for each service, telling you exactly what the prayers will be, what the songs will be, and they have books in which to find everything.
None of that is true at a Mandir (a Hindu temple). The statues of the gods will be set up either around the edges of a room, or staggered around the room so that there is plenty of space between each. There is a large, open space in the middle and chairs only around the edges for people too old to sit on the floor. You are visible to everyone there.
Unless you go for a particular function, everyone will be doing his own thing. You will see a few people sitting cross-legged in the center space meditating. You will see some people walking around to the different statues and touching the god's feet, ringing a bell, and/or prostrating themselves. There may be a Shiva lingam, on which people will pour water and touch it to the tops of their heads.
Even if there is a service going on, there will still be people wandering through and doing their usual devotions. The service might be in one corner of the room, near the gods that it is specifically for. These often involve a priest chanting in Sanskrit. They may be bathing and dressing the god or they my be performing puja, where rice, flowers and fruit are offered to the gods and people sip a special liquid or clap their hands in the air or touch their ears at particular times. There are no programs to tell you when these times are or what any of the Sanskrit means.
The woman I was sitting with yesterday asked me who I was there with. Generally that would be the only reason for a white person in a Mandir. I might be a kind of spiritual tourist, curious about an Indian friend's culture and there for an overview.
I am there to learn, so I don't give much detail about what I know already. She asked if I knew which god was which and I told her that I did. She asked if I knew any Indian languages and she was delighted that I was learning Hindi. She gave me the same advice every Indian I've told so far has given, "Watch Bollywood movies, it is the best way to learn."
I will continue to go to the Mandir and to observe until I know that I understand the rituals. I am there to learn, but not the basics, I am there for the advanced lessons now.