They exert influences in followings ways :
(i) by carrying out information campaign, organising meetings, filing petitions and etc.
(ii) Workers and Employees' association resort to organising protest activities like strikes or disrupting goverment programmes.
(iii)Business groups often employ professional lobbyist or sponsor expensive advertisements.

The relationship are as:
(i)Sometimes pressure groups are formed or led by the leaders of political parties or act as extended arms of political parties. 

(ii)Some political parties have grown out of movements. For example AGP in Assam and DMK & AIADMK in Tamil Nadu.

(iii)Most of the new leadership of political parties come from interest or movemernts groups.

They exert influence on politics of a democratic country in a variety of ways :

(i)They try to gain public support and sympathy for their goals and activities by carrying out information, campaigns, organising meetings, file petitions etc. Most of these groups try to influence the media into giving more attention to these issues.

(ii) They often organise protest like, strikes to disrupt government programmes. Workers’ organisations form pressure groups or movement groups and these may also participate in official bodies and committees that offer recommendation to the government.

(iii) Pressure groups and most of their movements, generally, have deepened democracy. Putting pressure on the rulers is not an unhealthy activity in a democracy if it is in good for all.

Pressure groups are organisations that attempt to influence goverment policies.
Examples:
1. Farmers’ Organizations: Bhartiya Kisan Union, etc.
2. Trade Unions: All India Trade Union Congress, Indian National Trade Union Congress and Bhartiya Mazdoor Sangh, etc.
3. Business Groups: FICCI, ASSOCHAM, CII, etc.