Fix typos in Sequence Basics (Part 2.1)

Part 2 - Sequence Basics/1. Creating a sequence.md

@@ -10,7 +10,7 @@ In previous examples we used `Subject`s and manually pushed values into them to
 
 ### Observable.just
 
-The `just` method creates an `Observable` that will emit a predifined sequence of values, supplied on creation, and then terminate.
+The `just` method creates an `Observable` that will emit a predefined sequence of values, supplied on creation, and then terminate.
 
 ```java
 Observable<String> values = Observable.just("one", "two", "three");
@@ -112,7 +112,7 @@ now.subscribe(System.out::println);
 
 ### Observable.create
 
-`create` is a very powerful function for creating observables. Let have a look at the signature.
+`create` is a very powerful function for creating observables. Let's have a look at the signature.
 
 ```java
 static <T> Observable<T> create(Observable.OnSubscribe<T> f)
@@ -226,7 +226,7 @@ The example above waits 2 seconds, then starts counting every 1 second.
 
 ## Transitioning into Observable
 
-There are well established tools for dealing with sequences, collections and asychronous events, which may not be directly compatible with Rx. Here we will discuss ways to turn their output into input for your Rx code.
+There are well established tools for dealing with sequences, collections and asynchronous events, which may not be directly compatible with Rx. Here we will discuss ways to turn their output into input for your Rx code.
 
 If you are using an asynchronous tool that uses event handlers, like JavaFX, you can use `Observable.create` to turn the streams into an observable