diff --git a/README.md b/README.md
index 8c022ab..57cf985 100644
--- a/README.md
+++ b/README.md
@@ -1259,18 +1259,27 @@ as key-value pair, document-oriented, etc.
 
 <details>
 <summary>What is a document? What is a collection?</summary><br><b>
+
+  * A document is a record in MongoDB, which is stored in BSON (Binary JSON) format and is the basic unit of data in MongoDB.
+  * A collection is a group of related documents stored in a single database in MongoDB.
 </b></details>
 
 <details>
 <summary>What is an aggregator?</summary><br><b>
+
+  * An aggregator is a framework in MongoDB that performs operations on a set of data to return a single computed result.
 </b></details>
 
 <details>
 <summary>What is better? Embedded documents or referenced?</summary><br><b>
+
+  * There is no definitive answer to which is better, it depends on the specific use case and requirements. Some explainations : Embedded documents provide atomic updates, while referenced documents allow for better normalization.
 </b></details>
 
 <details>
 <summary>Have you performed data retrieval optimizations in Mongo? If not, can you think about ways to optimize a slow data retrieval?</summary><br><b>
+
+  * Some ways to optimize data retrieval in MongoDB are: indexing, proper schema design, query optimization and database load balancing.
 </b></details>
 
 ##### Queries
@@ -1285,6 +1294,9 @@ as key-value pair, document-oriented, etc.
 
 <details>
 <summary>What is the difference between find() and find_one()?</code></summary><br><b>
+	
+  * `find()` returns all documents that match the query conditions.
+  * find_one() returns only one document that matches the query conditions (or null if no match is found).
 </b></details>
 
 <details>
@@ -2029,7 +2041,7 @@ This is where data is stored and also where different processing takes place (e.
 <details>
 <summary>What is a master node?</summary><br><b>
 
-Par of a master node responsibilites:
+Part of a master node responsibilites:
   * Track the status of all the nodes in the cluster
   * Verify replicas are working and the data is available from every data node.
   * No hot nodes (no data node that works much harder than other nodes)