I don't know how to get my Yongnuo flash to work on my Nikon D5100? - 1

I bought a Yongnuo external flash for my Nikon D5100 and when I put it on the hot shoe and take a picture the flash doesn't go off. I how do I get my camera to send the signal through the hot shoe to make the flash go off?

Which Flash should I purchase for my Nikon D3200?

I've shortlisted 2 Flashes for the use:
Metz Mecablitz 24 AF-1 Digital (for Nikon) Flash

OR

Nikon Speedlight SB-400 Flash

Let me know which one should I purchase from the above. If there are other options you wish to give me for purchasing the Flash for Nikon D3200, then do let me know.

Thanks in advance!

Added (1). The budget is till 7K INR

What kind of lens for photographing a wedding?

I have been asked to take wedding photos for the first time. One wedding will be in the summertime outdoors and the other in December and most likely inside. What kind of equipment works best for indoor events? I have a Nikon D90 with the kit lens and a prime portrait lens.
Also, since I have never taken wedding photos before, any additional advice would be appreciated!

I'm looking to create a film with my Nikon d3200 - tips?

I like how cameras change focus during filming - how is this achieved? I also like bokeh effect in the background with a focused forefront - how can I achieve this? Is there a camera mode (besides film record) I need to be in to achieve this?

Recommend a digital camera for me? - 1

I want a camera with:
-18-15mm lens, but with a good up close focus for flowers, etc
-Wi-Fi connectibility would be nice
-editing features on the camera
-small, portable
-under 500$
-interchangable lens
-i like nikon or sony cameras perferrably, although canons are okay too
-quick autofocus

Just to give some background info, I love the Nikon D5100, but i'm not sure if the 700$ price is worth it:/ I also like the Nikon D3100 and the Sony Alpha A57 but those two not as much.

I'm looking to create a film with my Nikon d3200 - tips? - 1

I like how cameras change focus during filming - how is this achieved? I also like bokeh effect in the background with a focused forefront - how can I achieve this?

Best but inexpensive lens for nikon d5100?

I would like to know if there's any lenses for nikon d5100 that is inexpensive but has a good quality. I'm a university student, I always bring my nikon d5100 with its 18-55mm lens and I love to take pictures like landscapes, buildings, night, and portrait.

Memory card in my Nikon D70 is screwed?

Some of the folders have question marks etc as the name, and they won't open. It seems the pictures are slowly being affected, and too won't open.

Any ideas?

What Image Sensor Swab Should I Use For A Nikon D3000?

Even if it's not a proper sensor swab i just need something to clean it with

Will this lens work on my nikon d5100?

Will this lens cooperate with my new d5100?
Nikon 55-200MM F4 - 5.6G AF-S DX Lens