Protein..

Get a when to eat after the workout.
Throughout the day include protein source in all meals.
Ex. Eggs , meat (fish and chicken are good lean meats) , nuts , almonds , milk ,
Protein bars are some good sources.

Just eat more eggs , meat,milk,peanut butter and so on... And yeah protein is really important ..

Really depends on what your current protein intake is? The general rule of thumb is 1g of protein per pound. Would also help to get an "in-body test", typically get mine done at Complete Nutrition. With this you will know what your average calories burned a day are regardless of excercising. This information will allow you to plan your caloric in take throughout the day. Typically shoot for 100-200 more calories than you are burning daily + excerise. This should allow you slowing gain weight while leaning out.

eating chicken breasts, if you dont have to money to intake a lot of protein from foods everyday, try protein shakes! I recommend whey protein

Peanuts are shit.
Best nuts are macadamia, almonds, hazelnuts, pistachios.
If you want to stay lean, make sure you eat healthy fats like avocado, fish/fish oil, you need that Omega 3.

If protein is your focus. Make your proteins your priority when you shop. Eggs, peanut butter, tuna, beans are always the best cheaper choices for protein although you have to watch your fats with peanut butter. Also check slickdeals they usually have deals on protein powders which is another way to get protein so you won't have to focus solely on spending on food. I love thos $ packs of tuna they usually have about 14g of protein.

walnuts will make you gain, lots of calories and protein. they are good for you aswell.

i think the best its whey protein

Protein intake is not importan as calorie surplus is. You should eat 1.5 - 2.2g protein per kg of your bodyweight. But most important thing is to eat more, you can calculate your calorie intake on google, and then try to make your own mealplan and stuff. Thats how I did it, and still doing. Im eating ca 3300 kcal daily, 175g proteins, ca 300g carbs and ca 100g healthy fats daily. And fruits and stuff ofcourse.

Not only protein, you have to increase carbs and fat to gain weight fella.

Eggs, Fish, Soya Milk, Lentils are good protien source

I usually eat food rich in protein, i take protein in powder and i might eat a protein snack

If you want to put on weight, the last thing you should be looking to get is protein powder... You clearly seem like a beginner (no offence) so the primary thing you should be looking at is the food you are eating.

You should post your current weight / age. However, eating more chicken breast / rice / vegetables will be the best way to put on lean mass. If you're looking to just put on weight in a more general term, try eat more calorie dense food to ensure you're in a constant caloric surplus.

Protein powder is a SUPPLEMENT and should be treated as such. Only use it when you're not meeting your daily protein requirements. Sometimes, due to my busy schedule I have to skip one of my meals which means I'm not hitting my daily macros, as a result, I'll take protein powder out of convenience, not out of necessity. Too many young kids thinking that protein powder is going to make them look like Phil Heath... Nail your diet --> then look towards incorporating supplements into your daily regime to further enhance your performance in the gym / recovery time and physique as a whole ^.^

drink 600ml of milk with every meal - 600ml x3 times per day is 60g protein easy