Verify current user access on current site

In this blog we will see how if current user having permissions a site

string webUri = //your site url;
using (ClientContext context = new ClientContext(webUri)) {  
    Web rootWeb = context.Site.RootWeb;
    context.Load(rootWeb);
    BasePermissions permission = new BasePermissions();
    permission.Set(PermissionKind.ManageWeb);
    ClientResult result= rootWeb.DoesUserHavePermissions(permission);
    try
    {                
        context.ExecuteQuery();
        if(result.Value){
            Console.WriteLine("You have access");
        }
        else{
     Console.WriteLine("You don't have access"); 
        }
    }
    catch(Exception ex)
    {
        Console.WriteLine("You don't have access");
    }
} 

Here basePermissions.Set(PermissionKind.ManageWeb); refers to access on web. Microsoft has provided more permissions levels we can verify.

Refer MSDN