I've used Guided Reading. Our whole reading program is Teacher's College Reading Workshop which starts with a 10 minute mini-lesson and then involves students independently reading trying the mini-lesson strategy and during that time the teacher can do individual conferring with students, or pull a group of students for a Guided Reading group lesson
Guided Reading lesson is where the students in the group are all at the same reading level (Guided Reading uses Fountas & Pinnell reading level letters) so generally in that group you are all working on a book together. Guided Reading group lessons last about 15-20 minutes.
When the students come to their Guided Reading group lesson, first you do a Pre-Reading to introduce the day's objective (what reading strategy you'll focus on today) and introduce a new book (or remind them where they left off in the book the other day), make predictions, etc. Then there's Reading where you can have them silently read the next chapter or pages X-X. You can have 1 student at a time read aloud to you while the others are reading silently, with younger grades you can have students take turns reading pages out loud as a whole group instead of silently reading, and you can prompt them/stop and ask them questions as they're reading.
Then there's Post-Reading where you have a discussion about what they read, and then give them a task, maybe have them answer a question in their reading response journals (a higher leveled group can be sent back to their seats to do this) or fill out a worksheet demonstrating their knowledge of the reading strategy applied to the book, or read the next chapter/pages and be ready to discuss the next day.
So basically Guided Reading is working with small groups based on reading level