You can send an InMail by clicking the Send InMail button in the top section of a member's profile or from search results. If you don't see this option, move your cursor over the Down arrow in the top section of their profile and select Send [Name] InMail.
InMail credits let you directly message members you're not connected to.
If you have a Basic (free) account, you must upgrade to a Premium account to use InMail credits.
If you have a Job Seeker, Business Plus or other legacy type of premium subscription and want more InMail credits than the number you've been allotted, you can always purchase up to 10 more. Note that additional InMail purchases outside of the monthly allotment are not available to Sales Navigator and Recruiter account holders.
Compare account types to find an account that meets your needs.
Learn more about InMail expiration and renewal.
You don't need to use an InMail to send messages to your 1st degree connections. Just click the button in the top section of your connection's profile that reads Send a message.