Here in the following snippet
Schema.getGlobalDescribe() returns the map with all sobject types in our org
By using this we can get Sobject type based on api name of object as in second line of snippet.
After getting the sobject type we can get the all the describe result of that object using "getDescribe()" method as in the third line of snippet.
Then we can get all field from that object by using "fields.getMap" as in the the
fourth line of snippet.
Map<String, Schema.SObjectType> m = Schema.getGlobalDescribe() ; Schema.SObjectType s = m.get('API_Name_Of_SObject') ; Schema.DescribeSObjectResult r = s.getDescribe() ; Map<String,Schema.SObjectField> fields = r.fields.getMap() ;