Hello I am new here and what I am wanting to do is build a irrigation control to control water valves for watering at times I want and duration also would like to control via wifi on my home network and monitor via android on my phone, am new to arduino so any help would be great.
I recommend you first decide how you will be communicating between the network and the Arduinos. It sounds like you are going to use WiFi. There are other options but I think that's a reasonable decision. So you have a few options for adding WiFi communication to an Arduino.
The cheapest option will be to use an ESP8266 board directly programmed. This microcontroller has built in WiFi support. I would recommend the WeMos D1 Mini board because it's the smallest and cheapest complete board for this purpose but there are other options, including the use of the ESP8266 module by itself with the addition of any other necessary components. The ESP8266 is a bit different than the traditional Arduino boards so you may find that some libraries or example code is not compatible but it does have very good community support. The ESP8266 also has 3.3 V logic. Although very standard, you will find that the accessories commonly used with Arduino tend to use 5 V logic and thus may need level shifting to work with the ESP8266. Whether this is an issue really depends on the components your project requires. It will give you no problems for simply controlling a valve. There is only one analog pin on the ESP8266, which could be limiting if you wanted to connect multiple analog sensors.
Another option is to use a standard Arduino board such as Uno, Leonardo, Pro Mini, Pro Micro, etc. with an ESP8266 module connected only for use as a WiFi module. The advantage of this approach is you will be able to use the massive amount of libraries/examples/tutorials/etc. written specifically for these boards. They have 5 V logic and multiple analog inputs. The disadvantage is it will increase the cost and size of the project, those boards are much less powerful than the ESP8266 and have less memory. Some people also find it quite difficult to get the Arduino communicating with the ESP8266, though I have had no problems.
Arduino sells a couple different WiFi boards and shields. The most recent board is the MKR1000. This uses a more modern microcontroller than the AVR microcontroller found on the classic Arduino boards such as Uno. This means that you may find that some code written specifically for AVR is not compatible with MKR1000. It has 3.3V logic.
Arduino.org sells a board named Uno Wifi that has an ESP8266 built in. Communication with the ESP8266 works differently from the usual approach so you would need to use sketches and libraries specifically written for that board.
There are some other 3rd party WiFi options but I'm not familiar with them and don't see them mentioned here often so I can't really list anything specific.
Once you have decided on which of those choices you will use for your project buy one or two. It's always nice to have a spare, especially with the $3 USD w/ free shipping WeMos D1 Mini clones why not buy two? If you're going with the more expensive options it might be worth starting with only one until you have verified this is the approach for your final project.
After the hardware arrives start with the examples included with the Arduino IDE (File > Examples) to get a good understanding of the basics of programming the Arduino. You don't need to worry about the valve yet, just blink the LED on the Arduino to simulate turning the valve on and off. The code will be the same either way, only the hardware will change. Once you can successfully control the LED via your Arduino, network, and monitor it on your phone you will be ready to proceed with buying the parts for the project.
Write out a BOM (bill of materials) for the project. Don't forget things like enclosures and mounting hardware. You may want to do test purchases of some of the more expensive components before purchasing enough for the entire system, other components may be sold in quantity so you will just end up buying enough for the whole system at once.