Implement saving and opening the saved file in the project

First, let's understand what serialization / deserialization is:

Serialization (in programming) (born serialization) is the process of translating any data structure into a sequence of bits. The inverse of the serialization operation is the deserialization (structuring) operation ( deserialization ) - restoring the initial state of the data structure from the bit sequence.

Source: Wikipedia .

We can safely replace the byte sequence with any convenient form for us (XML, JSON, etc.). I personally love JSON and for this reason I will use it in the examples.

Suppose we have a certain collection Names , which contains some objects:

 List<string> Names = new List<string> { "Вася", "Петя", "Маша", "Аня" }; 

We need to serialize it into a convenient form and save it to a file:
* As I have already said, I will use JSON, and it is very easy to work with it using the Newtonsoft.Json library (install via NuGet).

 var jsonString = JsonConvert.SerializeObject(Names); File.WriteAllText("MyData.json", jsonString); 

After that, we will have created a file MyData.json , which will contain our serialized object in JSON format:

 ["Вася","Петя","Маша","Аня"] 

Now we do the opposite, extract the data from the file, deserialize it and get back the List<string> :

 var file = File.ReadAllText("MyData.json"); List<string> Names = JsonConvert.DeserializeObject<List<string>>(file); 

That's all, by such simple actions we “drive” the data into a file and then read it. The format, as well as the object can be different, this is how you learn and what is more convenient.
Good luck learning C #!