There are two ways to send a LinkedIn Invitation, one allows you to invite someone to connect who is already on LinkedIn and the other is to someone who isn’t on LinkedIn.
To connect with someone on LinkedIn who is already a member, first go to their profile by searching for them in the search box. When there profile opens select the option to ‘Connect’ which is next to the profile picture. You will be taken to a page where you will need to choose how you know the person. Be wary of using ‘Friend’ unless they are actually a friends as this can alienate someone.
When it comes to the body of the text make sure to customise it. Mention how you know the person, whether it is from a group, seminar or even through a friend. When you are happy select ‘send invitation’
The other way allows you to send an invitation email to someone that isn’t on LinkedIn already. To do this go to the image of a person and a plus sign at the top right of the page and select ‘Invite your contacts’. You can here enter your email and it will bring up a list of all the contacts you have on that account. Alternatively if you wish to invite someone else select ‘Any Email’ and then ‘invite by individual email’. This will open a box where you can type numerous emails, please be aware then when you select ‘Send Invitations’ it will send the bog standard invite message.