It depends on where are you uploading your pictures. Irrespective of the place, you watermark must be small enough not to cover much of your photo. You can keep your watermark mostly around bottom corner.  

The only thing you need to do so is a DSLR.

It also depends on  DSLR as to which type of AF technology  it uses or what are the diffrent types of focus points that the camera has.

And just automatically or manually focus your subject and you are ready to go.

By this you should be ok to focus on.

Use lense which has the lowest aperture.

Lower the aperture the you will get the nice blur background.

Or even if you dont have a good lense just put the aperture to your lowest.

Hope you will find it helpful.

In any lens, elements are the specific lens pieces used and how are they arranged to obtain a particular feature, the arrangement is the group. Lenses pieces are usually arranged in groups. In lens, say if it is a zoom lens, it will have more number of elements and groups, where as for a prime lens, it will have less number of groups and elements. 

Usually it is termed as the more number of groups and elements, the better the quality but it is not always true. Lens quality also depends on the type of glass, design mechanism, manufacturing process of the lens. So for a particular focal length, a prime lens would be better than the zoom lens.

Prime lenses usually perform better than zoom lenses.

1 Best way to click pictures on a mobile phone is by using grid mode available on every cell phonenow you just have to put 9 things in those 9 boxes which will result in beautiful composition 

2. The angle from where click picture

1. Shooting with 50mm lens can let you shoot at aperture as wide as 1.8 but a 18-55mm will allow you to shoot only at 5.0 aperture 
2. This difference itself is a huge deal. This means you can have the advantage of having faster shutter . Imagine shooting handheld at 1/15s with aperture f5.0 and then at 1/125s with aperture f1.8. This can be significant in low light conditions.

there are 2 ways of achieving focus

Using Autofocus

turn on the auto focus mode on your lens->then point at your subject->click shutter release button half way to lock the subject in focus->adjust your frame if needed WHILE HOLDING THE SHUTTER RELEASE BUTTON->press the shutter release button to take your photo with subject in focus

Using manual focus

turn on your manual focus on the lens->point at your subject->use the focusing ring to adjust focus according to your eye->press shutter release button to click the photo

Its the Aperture that is denoted by f and it is also known as f stop.

The diffrence between both  is that f/1.4 lets you get more light to your image.

rather f/1.8 lets you get less light in your image.

More the aperture less the light and less the aperture more the light .

and one of the main use of it is the depth of the field.

Suppose you want your background to be blurred at a good rate then use as low apeature as you can.

Hope you will find it helpful.