Salesforce provides ready to use tools to do so. In order to import data within Salesforce from an external CSV (comma separated value) file, you need to know the Salesforce object (equivalent of a table in a RDMS but much more than that..) and fields on the object (equivalent to columns of a table) to which you intend to push this data to.
I am assuming that the total number of records that you are attempting to import are less than 50,000 in number. These are the 3 most widely used tools that you could use here and do not imply an additional cost.
Data Import Wizard - You will be able to access this tool by logging into your Salesforce instance and navigating to Setup > Data Import Wizard. This is limited to importing a maximum of 50,000 records only. Refer the following link to know the specifics of importing records into Salesforce using this method - Import Data with the Data Import Wizard.
Data Loader - Data Loader is a client application used to import bulk data and perform DML operations on the Salesforce data. This tool will need to be installed locally on your machine before you can start using this. This utility comes in handy when you intend to insert or manipulate records greater than 50,000 in number. Refer the following link to know the specifics of installing and then importing records into Salesforce using this method - Data Loader
Workbench - External utility available over the web and popularly used by Salesforce Admins and Developers however this is not owned or managed by Salesforce itself. Login to the utility using the credentials for the Salesforce instance to which the records need to be imported. Navigate to data > Insert within workbench and follow the relevant steps. Refer the following link to access Workbench - Workbench.