You need to calculate how, on many days, you will board at least one train.

I get it to 3 days if you don't travel around in Switzerland:

Paris-Munich

Munich-Switzerland

Switzerland-Milan

The planning tool from Interrail/Eurail is crap so don't use it. Make your plan on paper or on a spreadsheet and calculate the number of travel days yourself. 

hi annaB, thank you for your warm reply it really helpful

it’s my first time traveling to Europe, is this eurailpass can be use inside the city? or just for passing through country?

is this eurail pass can be use around Switzerland?

i think i’m lack of insight haha

do you have any suggest for first time traveling in Europe?

sorry if my English is not really well

thank you ^^

The pass works on trains of most companies. Some low-cost companies like Ouigo or Flixtrain are not included.

Not valid on buses, trams, subways.

The pass can (and should !) be used within Switzerland, it is great value ! The vast majority of railways are included except Interlaken - Grindelwald/Lauterbrunnen. Otherwise you often get 25-50% discount on mountain railways. Boats on Lake Thun and Brienz are included !

Now you only have to decide how many days you might need.