updated core concepts

Author: 0hsn

docs/05-References/050-concepts.md

@@ -1,26 +1,42 @@
 ---
-title: Concepts
+title: Core concepts and usage
 ---
 
 This page describes some key concepts before you use **`chkware`**.
 
 There are two parts to **`chkware`** tool.
 
-1. The command line tool `chk`, that you can run. `chk` supported sub-commands are listed below.
-2. The specification files those contains configuration in _YAML based dsl_. These files have extension `.chk`.
+1. The command line tool `chk`, that you can run. `chk` [supported sub-commands](#supported-sub-commands) are listed below.
+2. The [specification files](#specification-files) those contains configuration in _YAML based dsl_. These files have extension `.chk`.
 
 ### Supported sub-commands
 
 - `chk http [--result] [FILE].chk`
-  > Purpose of this sub command is to run a spec. file written in format supported by [http spec. file](http-reference). After you execute this command `chk` should make request by given request format, and display the response. You can also customize the response with `request`.`result` key.
+  
+  This sub command runs a file written in [http specification file](http-reference) format.
+  
+  After you execute this command `chk` should make request by given request format, and display the response. You can also customize the response with `request.result` key. see [usage](/Examples/http-examples#request-with-form) and [documentation](/References/http-reference).
 
+  **[Options]**
   - `--result` <small>***optional***</small>: When you put this option, the you'll see only the result.
-  - `[FILE].chk` <small>***required***</small>: File that you want to execute. See below for details.
+
+  **[Arguments]**
+  - `[FILE].chk` <small>***required***</small>: File that you want to execute.
+
+- `chk testcase [FILE].chk`
+  
+  This sub command runs a file written in [testcase specification file](testcase-reference) format.
+  
+  After you execute this command `chk` should re-use `http` utility to request as per given structure on the file, execute test assertions, and display the result of the assertions. See [example](/Examples/testcase-examples).
+
+  **[Arguments]**
+  - `[FILE].chk` <small>***required***</small>: File that you want to execute.
 
 ### Specification files
 
-Test specification files are written in YAML, having file extension `.chk`. So, before you start writing any specification file, you should have a proper introduction to YAML, if you do not have already. Here is a fine [YAML cheatsheet](https://quickref.me/yaml) to grasp some knowledge. We are using this specific extension (`.chk`) so these files do not make you confuse in typical project layout.
+Test specification files are written in YAML, having file extension `.chk`. So, before you start writing any specification file, you MUST have a proper knowledge of YAML, see [YAML cheatsheet](https://quickref.me/yaml). We are using this specific extension (`.chk`) so these files do not make you confuse in typical project layout.
 
 > In the future evolution path of **chkware** we are going to introduce more and more specification options and specification types and versions.
 
-- [Http specification file](http-reference)
+- [Http specification file](http-reference)
+- [Testcase specification file](testcase-reference)