I was in Tokyo earlier this year and one thing I noticed people saying a lot was something that sounded like anno.
It sounded to me like an uncertain pause in a sentence, like:
I'd like, er... (anno) one of those please
Is there an equivalent in Japanese of the English 'er...'?
If so, how would I use it in a basic Japanese sentence such as ordering drinks?
You heard あのう anō, which is a bit like "ahem" or "well", used to get someone's attention and prepare the listener to what you're going to say.
A better substitute for "er" would be えっと／ええと. To order a beer you could say
えっと、生一。
えっと、とりあえず生で。
(if you're asked by the waiter).
If you're trying to get the waiter's attention, it's better to use あのう.
Also check
You heard right (more or less), and you're assumption is right. "I'd like... uh... a beer". "Etto" (sometimes with the E longer than other times) also works similarly and is more formal... if you can believe that.
It can also be used to get someone's attention, by simply stating either rather blankly. Tone and other words appended can change this from harmless to angry.
Another usage is just to buy time. Translation wise it would probably the same, but also colloquially could sound more like, "Let's see..." like you might say while looking over a menu while your server anxiously awaits you to decide.
Basic usage will sound different since the variable in the sentence (drinks in this case) are located in a different part of the sentence. For example if you're asked what you want, a valid reply might be.
えっとですね。。。ビールをお願いします。
In short... both are pretty flexible.
