This site is dedicated to learning to give meaningful, helpful critique but sometimes people confuse that with Beta-reading so I thought I'd just post a few thoughts here about the differences.
So to start with what is Critique? Critique is defined on dictionary dot com as "a detailed evaluation or review of a literary piece" To me this means that people who want critique want details about what is wrong with thier piece. Obviously if a critic were only to point out the things that were wrong with the piece people would soon loose confidence and stop writing so I try to give details about what's right with the piece too.
The key here is | detail | be specific and don't be afraid to make suggestions. When I give critique I try to point out that the suggestions I give are only my opinion and aren't the only way to get where the writer wants. I also believe that it's a good idea to give reasons why things need to be improved or what you like about them. Just saying "I liked this piece" is NOT a critique it's a comment. Everyone needs critique, including "professional" writers, it's the best way to improve your writing.
On the other hand though some people aren't looking for details, they are looking for an overall view. This is known as beta-reading. Essentially what they are looking for is someone to point out any glaring plot errors or errors in continuity. The most common error that people have in their writing is tense errors where they have changed from present tense to past and back again (as I just did) or vice versa.
Over the length of a novel sometimes it is difficult to keep everything in line so occasionally a character might be described early on in the story as having green eyes and later on as having blue eyes. These are the kinds of things that readers pick up on but a writer might not because they know what they "intended" to write. They just need someone to check what they actually wrote.
When you have finished beta reading the writer isn't really looking for reams of notes about what you liked and what you didn't, they just want the facts telling them where they changed something they shouldn't have or where there's a typo etc.
Myself I tend to view beta-reading as a "final brush" before a piece is completed. The last thing (except any corrections) that is done before it is sent for review by a publisher / agent who will then say if it's good enough or not to start the process of being published.
Very few people need beta-readers. The world of publishing is not an easy world to get into and people need to be not only good but exceptional (or bloody lucky usually both) to get into the world properly. Many people think that they are worth publishing but really aren't ready for it with too poor writing / story telling skills to pull it off. Many of these people go down the route of "self publication" which is very popular and easy to do these days. I think that even people going down this route need critique because there is always room for improvement, before they publish it though they should also have beta-readers who are not their friends so they will be honest with them.
I hope that helps a bit with how you look at pieces.