Q:

Can logos be made just by using a font rather than creating a logo image?

Most people make logo by creating an image for it. I don't want that since I don't know Photoshop and I may make it ugly.
Can logos be made just by using a font rather than creating a logo image?

A:

Just use a font

I'd say no. That's not a logo, that's simply a line of type set using a font anyone can use. There's nothing identifying or unique about it. That is not a logo in my opinion.
Companies which use a typeface designed logo actually design the type. It's rare you'll ever see a company use some typeface which is straight from someone choosing a font in an application menu. That's not design. That's not a logo. That's just typing.
Can you create a logo which is type. Yes, absolutely. But it should involve more than simply picking a font.

A:

Certainly. As @Bakabaka already mentioned, many companies do this. 
Here's a great example:

But I'd also like to address another point:

I don't want that since I don't know Photoshop and I may make it ugly.

Don't just use plain text because it's easy, do it if it makes sense.
EDIT
Another thing to keep in mind is that you don't need anything complicated when it comes to logos. Look at the Target logo, which consists of some circles to make a target, and then they write their company's name with Helvetica.

A:

Can logos be made just by using a font rather than creating a logo
  image?

To answer your question yes they can.
I didn't see it noted but some companies will design their own font to be used as a typographic design similar to this:

If you are considering making a logo based on typography it would be a good idea to understand typography.  Several good reads here:

Book: The Elements of Typographic Style
Site: Thinking With Type
Site: What is typography? Learn the basic rules and terms of type!
Site: Five simple steps to better typography
Site: Know Your Type

Last but not least just as much time can be put in a typographic logo VS a symbolic logo or Iconic logo.

